Ammonia separation method and zeolite

ABSTRACT

Provided is a method for separating ammonia gas using zeolite membrane having excellent separation stability at a high temperature capable of separating ammonia gas from a mixed gas composed of multiple components including ammonia gas, hydrogen gas, and nitrogen gas to the permeation side with high selectivity and high permeability. Also provided is a method for separating ammonia by selectively permeating ammonia gas from a mixed gas containing at least ammonia gas, hydrogen gas, and nitrogen gas using a zeolite membrane, wherein the ammonia gas concentration in the mixed gas is 1.0% by volume or more.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. application Ser. No. 17/153,961 filedJan. 21, 2021, allowed, which is a continuation of U.S. application Ser.No. 16/713,360 filed Dec. 13, 2019, now U.S. Pat. No. 10,946,333, whichis a continuation of International Application PCT/JP2018/023042, filedon Jun. 15, 2018, and designated the U.S., and claims priority fromJapanese Patent Application 2017-117862 which was filed on Jun. 15,2017, Japanese Patent Application 2017-239295 which was filed on Dec.14, 2017, Japanese Patent Application 2018-007414 which was filed onJan. 19, 2018, Japanese Patent Application 2018-007415 which was filedon Jan. 19, 2018, and Japanese Patent Application 2018-007416 which wasfiled on Jan. 19, 2018, the entire contents of which are incorporatedherein by reference.

TECHNICAL FIELD

The present invention relates to a method for separating ammonia byusing a zeolite membrane to selectively allow ammonia gas to permeate,from a mixed gas composed of a plurality of components including ammoniagas, and hydrogen gas, and/or nitrogen gas. The present inventionrelates to a zeolite membrane that effectively separates ammonia from amixed gas composed of a plurality of components including ammonia gas,and hydrogen gas, and/or nitrogen gas even under high temperatureconditions.

BACKGROUND OF THE INVENTION

In recent years, membrane separation methods and membrane concentrationmethods using membranes such as polymer membranes and zeolite membraneshave been proposed as methods for separating gas mixtures.

While a polymer membrane has a feature that it is excellent inprocessability into, for example, a flat membrane or a hollow fibermembrane, there remains a technical problem that a polymer membrane iseasily swelled and has low heat resistance. A polymer membrane has lowresistance to reactive chemicals, and there remains a technical problemthat a polymer membrane easily deteriorates due to adsorptive componentssuch as sulfides. Furthermore, since a polymer membrane is easilydeformed by pressure and the separation performance is thereby lowered,a polymer membrane is not practical in separation of ammonia under hightemperature conditions, which is one of the problems of the presentinvention.

In response to this, various inorganic films having favorable chemicalresistance, oxidation resistance, heat stability, and pressureresistance have been proposed in recent years. Among them, a zeolitemembrane is expected to be a highly durable separation membrane that notonly selectively allows specific molecules to permeate, but also enablesseparation and concentration over a wider temperature range than polymermembranes since a zeolite membrane has ordered sub-nanometer pores andfunctions as a molecular sieve. Such a zeolite membrane is usually usedas a zeolite membrane composite in which zeolite is formed into amembrane on a support made of an inorganic material. For example, it hasbeen found that when a reaction mixture having a specific composition isused when forming a zeolite membrane on a porous support by hydrothermalsynthesis, the crystal orientation of zeolite crystallized on thesupport is improved, and a dense zeolite membrane that combinespractically sufficient throughput capacity and separation performance inseparation of a mixture of an organic compound and water can be formed(Patent Documents 1 to 3).

In general, a zeolite membrane such as an A-type membrane, a FAUmembrane, an MFI membrane, an SAPO-34 membrane, or a DDR membrane isknown as a zeolite membrane for gas separation, and a zeolite membranecomposite for gas separation exhibiting high throughput capacity andseparation performance has been proposed for separation of gasdischarged from thermal power plants or petrochemical industries such asseparation of carbon dioxide and nitrogen, carbon dioxide and methane,hydrogen and hydrocarbon, hydrogen and oxygen, hydrogen and carbondioxide, nitrogen and oxygen, paraffin and olefin, or the like (Forexample, Patent Document 4).

On the other hand, regarding the separation of ammonia gas from hydrogengas and nitrogen gas of the present invention, application of membraneseparation, for example, to an ammonia production process by theHaber-Bosch process, one of industrially important processes is expectedin recent years. One of the characteristics of the Haber-Bosch processis that although such an ammonia generation reaction is an equilibriumreaction, and thermodynamically, a reaction under high pressure and lowtemperature conditions is preferable, high pressure and high temperatureproduction conditions are generally required in order to ensure acatalytic reaction rate. Since unreacted hydrogen gas and nitrogen gascoexist with ammonia gas in a mixed gas to be generated, in a step ofrecovering the ammonia gas as a product from the generated mixed gas, itis necessary to cool the mixed gas to about from −20° C. to −5° C. tocondense and separate the ammonia (Non-Patent Documents 1 and 2). Inparticular, in the latter case, the concentration of ammonia gascontained in the generated mixed gas is inevitably low due to thereaction equilibrium limitation described above, and therefore, in astep of cooling and separating ammonia from the generated mixed gas, thecooling efficiency is poor and a great amount of energy is consumed. Inthe process, it is necessary to separate a large amount of mixed gas ofhydrogen gas and nitrogen gas from the generated mixed gas and recyclethe separated gas to a reactor as raw material gas, and it is necessaryto increase the pressure of the cooled, unreacted mixed gas to apredetermined pressure and the temperature of the gas to a reactiontemperature, and therefore, the actual situation is that the energyconsumption at the time of production is further increased.

To avoid such an energy intensive process, a process that efficientlyrecovers high-concentration ammonia gas by replacing a cold condensationseparation method in a purification step with a separation method usingan inorganic membrane has been proposed (Patent Documents 7 and 8).

Examples of the method for separating mixed gas containing highconcentration ammonia gas from mixed gas of hydrogen gas, nitrogen gas,and ammonia gas include: 1) a method of using a separation membrane toselectively allow hydrogen gas and/or nitrogen gas in the mixed gas topermeate; and 2) a method of using a separation membrane to selectivelyallow ammonia gas in the mixed gas to permeate.

As the former method for selectively allowing hydrogen gas and/ornitrogen gas to permeate, a method of using a polycrystalline layer ofvarious zeolites (Patent Document 5) and a method of using a molecularsieve film (Patent Document 6) have been proposed. In Patent Document 7,a method for selectively allowing hydrogen gas and/or nitrogen gas topermeate and a method for selectively allowing ammonia gas to permeateare described, and a separation method for separating at least onecomponent of hydrogen gas, nitrogen gas, and ammonia gas from agenerated gas that is a mixture of hydrogen gas, nitrogen gas, andammonia gas, using a separation membrane in which a silica-containinglayer is layered on a ceramic substrate is proposed. Specifically,Patent Document 7 describes, in a schematic flowchart in which aseparation membrane is applied to ammonia production, that sincehydrogen gas selectively permeates a silica membrane under hightemperature conditions, two separation membranes are installed, thehydrogen gas is separated to the permeation side by the first separationmembrane, and from nitrogen gas and ammonia gas that have not permeatedthrough the first separation membrane, the ammonia gas is separated tothe permeation side by the second separation membrane. Patent Document 7also describes that in order to separate ammonia gas from a mixed gas ofhydrogen gas and ammonia gas, it is necessary to use a low temperaturecondition such as 50° C., and the ammonia gas concentration in the mixedgas needs to be higher than 60% by mole.

On the other hand, in addition to Patent Document 7, as the lattermethod for selectively allowing ammonia gas to permeate, an efficientammonia separation method for separating ammonia gas from a mixed gas ofammonia gas, and hydrogen gas, and/or nitrogen gas by using a specificzeolite having an oxygen eight-membered ring is proposed (PatentDocument 8). Here, a method for separating ammonia gas by designing aspecific zeolite membrane composite, and by using a molecular sieveaction utilizing the pore diameter of the zeolite is proposed. Although,in general, ammonia is used as a probe molecule that is adsorbed at anacid site in a temperature-programmed desorption method that measuresthe acid amount of zeolite, and the peak top temperature reaches as highas about 480° C., the adsorbed ammonia has a property of desorbing dueto temperature rise (Non-patent Document 3), while Patent Document 8discloses that the permeation performance of ammonia gas can becontrolled by controlling the adsorption ability of ammonia to zeoliteby ion exchange of zeolite. Patent Document 8 deals with a problem ofclogging of zeolite pores by ammonia when ammonia gas permeates, and atechnique that avoids this problem is disclosed in Examples thereof. Inthe separation technique of Patent Document 8, it is proposed that atechnique of permeating ammonia gas by using a molecular sieve actionutilizing the pore diameter of zeolite while using zeolite thatsuppresses adsorption of ammonia and suppressing clogging of ammonia inthe pores is effective.

On the other hand, as an ammonia synthesis method, an innovativeproduction process has been developed in recent years, and specifically,a production process that uses an electride catalyst supportingruthenium metal and exhibits extremely high catalytic activity evenunder low temperature conditions (from 340 to 400° C.) has been reported(Patent Document 9).

CITATION LIST Patent Documents

-   Patent Document 1: JP 2011-121040 A-   Patent Document 2: JP 2011-121045 A-   Patent Document 3: JP 2011-121854 A-   Patent Document 4: JP 2012-066242 A-   Patent Document 5: JP H10-506363 T-   Patent Document 6: JP 2000-507909 T-   Patent Document 7: JP 2008-247654 A-   Patent Document 8: JP 2014-058433 A-   Patent Document 9: WO2015/129471

Non Patent Documents

-   Non Patent Document 1: The Chemical Society of Japan, 6th edition,    Chemical Handbook, Applied Chemistry I, Maruzen Co., Ltd. (2003), p    581-   Non Patent Document 2: The Society of Chemical Engineers, Japan,    Compilation of Chemical Processes 1st Edition, Tokyo Kagaku Dozin, p    153-   Non Patent Document 3: Naonobu Katada, Miki Niwa, Zeolite Vol. 21 No    2, Japan Zeolite Association (2004), p 45-52

SUMMARY OF INVENTION Technical Problem

However, in a method for selectively allowing hydrogen gas and/ornitrogen gas in a mixed gas containing hydrogen gas, nitrogen gas, andammonia gas to permeate, what is recovered through a separation membraneis hydrogen gas and/or nitrogen gas, and an essential problem of thismethod is that a process for first separating hydrogen gas and/ornitrogen gas from a mixed gas containing relatively high concentrationammonia gas is employed. In other words, in the step of separatinghydrogen gas and/or nitrogen gas, a considerable amount of ammonia gaspermeates along with the permeating hydrogen gas and/or nitrogen gas,and therefore, there is a problem that an economical process cannot berealized unless the considerable amount of permeated ammonia isrecovered. For example, when the technique of Patent Document 7 isadopted, for completing an economical process, a step of separatingammonia gas from a high-concentration hydrogen-mixed gas containingammonia gas permeated through a first-stage separation membrane and amixed gas of nitrogen gas and ammonia gas not permeated is essential.Specifically, this method is not only a complicated process forseparating ammonia gas from a mixed gas of hydrogen gas, nitrogen gas,and ammonia gas in at least two stages, but also a process requiring astep of recovering ammonia from both the mixed gas permeated in thefirst stage and the non-permeated mixed gas to be completed as aneconomical process, which is even more complicated. In order toessentially solve these problems, it is necessary to separate hydrogengas and nitrogen gas from relatively high concentration hydrogen gas anda mixed gas containing nitrogen gas and/or a mixed gas containingrelatively low concentration ammonia gas, but such a process cannot be aproductive ammonia production process and is not practical.

Furthermore, in the process of recycling the hydrogen gas separated tothe permeation side by the first-stage membrane under high temperatureconditions proposed in Patent Document 7, there is a problem thatrequires energy for boosting the hydrogen gas, and further, in theseparation of nitrogen gas and ammonia gas from the second-stagemembrane, the permeability of ammonia gas is not sufficient, and themembrane area may be increased. Further, in the method of patentdocument 7 which separates hydrogen gas used as a raw material gas froma mixed gas of hydrogen gas, nitrogen gas, and ammonia gas under hightemperature conditions, for example, when the separation membraneaccording to one embodiment of the present invention is directlydeposited to the ammonia synthesis reactor to synthesize ammonia, sincethe raw material gas permeates, the reaction becomes disadvantageous dueto the restriction of the reaction equilibrium described above, and highconcentration ammonia gas cannot be generated. From the above point ofview, with a method of using such a separation membrane to selectivelyallow hydrogen gas and/or nitrogen gas in a mixed gas of hydrogen gas,nitrogen gas, and ammonia gas to permeate, the energy cost at the timeof production rises and the process becomes complicated, and therefore,it is difficult to find an advantage of introducing a separationmembrane into an ammonia production process.

On the other hand, a technique of using a separation membrane toselectively allow ammonia gas in a mixed gas of hydrogen gas, nitrogengas, and ammonia gas to permeate is effective as a technique for solvingvarious problems described above. However, in the ammonia gas separationmethod using a separation membrane in which a silica-containing layer islayered proposed in the known document 7, it is shown that a mixed gashaving an ammonia gas concentration higher than 60% by mole needs to beused, and that the mixed gas needs to be cooled to 50° C. in order todevelop a blocking effect by ammonia, and the ammonia gas separationability is such that ammonia gas is slightly more permeable thanhydrogen gas. In such a process, there is, in the first place, a problemof how to prepare a mixed gas having an ammonia gas concentration higherthan 60% by mole, and even if such a mixed gas is prepared, the gasneeds a great deal of energy for cooling, and therefore, it is difficultto complete an economical process.

On the other hand, the method of separating ammonia gas from a mixed gasof ammonia gas, and hydrogen gas, and/or nitrogen gas by using aspecific zeolite having an oxygen eight-membered ring proposed in PatentDocument 8 can be an effective technique applicable to industrialprocesses without the above-described restrictions in order to permeateammonia gas. However, in the method for separating ammonia by using amolecular sieve action utilizing the pore diameter of zeolite proposedin Patent Document 8, the permeance ratio (ideal separation factor)between ammonia gas and nitrogen gas is only about 14 at most, and thepermeation performance is not sufficient. Further, Patent Document 8proposes that the permeance ratios of hydrogen gas and ammonia gas tonitrogen gas are obtained individually, and by comparing these ratiovalues, basically, ammonia gas in a mixed gas of hydrogen gas, nitrogengas, and ammonia gas selectively permeates, but especially in view ofthe permeance ratio of ammonia gas to that of hydrogen gas, thepermeation performance is not sufficient, and the effectiveness of theabove-described ammonia gas separation by using a molecular sieve actionutilizing the pore diameter is limited. Furthermore, in Patent Document8, ammonia gas is separated from a mixed gas of nitrogen and ammonia gasat 140° C., and when comparing the permeance of various gases before andafter ammonia gas permeation, the permeance value of any gas increasedafter permeation, and therefore, there remains a problem that thedurability of a zeolite membrane is impaired even under relatively lowtemperature conditions such as 140° C. Regarding these problems, inorder to efficiently allow ammonia gas to permeate using a zeolitemembrane, since ammonia essentially has the adsorption ability tozeolite, it is also necessary to appropriately combine the compositionof a supply gas mixture and the temperature at which the gas isseparated. However, in Patent Document 8, there is no description orproposal for appropriate separation conditions, and a method forseparating ammonia from a mixed gas of hydrogen gas, nitrogen gas, andammonia gas, or a mixed gas of hydrogen gas and ammonia gas is notdemonstrated.

On the other hand, regarding an ammonia production process, as in PatentDocument 9, in recent years, a highly active catalytic process ofammonia production has been reported even under low temperature and lowpressure conditions, and is expected as a process for reducing energyconsumption during production. However, with this innovative productionprocess alone, because of the reason that the ammonia generationreaction is an equilibrium reaction as described above, a mixed gascontaining high concentration ammonia gas higher than the equilibriumcomposition cannot be generated due to the limitation of reactionequilibrium, and essentially, the above-described problems such asreduction of energy consumption during production including a recoveryprocess of generated ammonia and a recycling step of raw material gascannot be solved.

The present invention has been made in view of the above-describedconventional situation, and an object thereof is to provide a method forseparating ammonia, in which ammonia gas can be separated from a mixedgas composed of a plurality of components including ammonia gas, andhydrogen gas, and/or nitrogen gas by allowing the mixed gas to permeatethrough a zeolite membrane with high selectivity and high permeability,and which is excellent in high-temperature separation stability andlong-term operation stability.

Solution to Problem

The present inventors have further studied separation of ammonia using azeolite membrane to solve the above-described problems, and found thatthe ammonia permeation selectivity gas permeating through a zeolitemembrane is considerably improved when the concentration of ammonia gasin a mixed gas of hydrogen gas, nitrogen gas, and ammonia gas is higherthan a specific amount. The present inventors have also found that whenone aspect of the present invention is used, ammonia gas separationperformance can be stably maintained even under temperature conditionsexceeding 200° C. Surprisingly, the present inventors have also foundthat a similar effect is exhibited in a zeolite such as MFI having alarge pore diameter relative to the molecular sizes of hydrogenmolecules, nitrogen molecules, and ammonia molecules. In other words,since permeating ammonia gas clogs pores of zeolite, Patent Document 8proposes a method for separating ammonia by designing an ammonia gasseparation/permeation membrane that avoids the clogging, and in thepresent invention, it has been found that, on the contrary, when amethod of actively adsorbing ammonia on zeolite is used, the ammonia gasseparation performance is considerably improved and the separationstability is improved, whereby the present invention has been completed.It has been also found that when a zeolite membrane different from thesilica membrane proposed in Patent Document 7 is used, ammoniaseparation performance can be stably maintained even under hightemperature conditions exceeding 50° C. and even 200° C., therebycompleting the present invention.

The first embodiment (Invention A) of the present invention has beenachieved based on such findings, and provides the following.

[A1] A method for separating ammonia by using a zeolite membrane toselectively allow ammonia gas to permeate, from a mixed gas containingat least ammonia gas, hydrogen gas, and nitrogen gas, wherein theammonia gas concentration in the mixed gas is 1.0% by volume or more.[A2] The method for separating ammonia according to [A1], wherein thevolume ratio of hydrogen gas/nitrogen gas in the mixed gas is from 0.2to 3.[A3] The method for separating ammonia according to [A1] or [A2],wherein the temperature at which ammonia is separated is from higherthan 50° C. to 500° C.[A4] The method for separating ammonia according to any one of [A1] to[A3], wherein the zeolite constituting the zeolite membrane is RHOzeolite or MFI zeolite.[A5] A method for separating ammonia, including a step of producingammonia from hydrogen gas and nitrogen gas, wherein ammonia is separatedfrom a mixed gas containing ammonia gas obtained in the production stepby the separation method according to any one of [A1] to [A4].

In order to solve the above-described problems, the present inventorshave further studied separation of ammonia gas by using a zeolitemembrane, and found that although, regarding the separation performanceof existing zeolite membranes for ammonia gas separation that canseparate ammonia gas more selectively and efficiently than existingsilica membranes, the permeance ratio (ideal separation factor) ofammonia gas and nitrogen gas was only about 14 at most, when a zeolitemembrane having a surface in which the molar ratio of nitrogen atoms toAl atoms determined by X-ray photoelectron spectroscopy (XPS) is in aspecific range is used, ammonia gas separation performance isconsiderably improved. The present inventors have also found that theammonia gas separation performance can be stably maintained even underhigh temperature conditions by using the present invention.Specifically, the present inventors have found that in order to separateammonia gas with high selectivity and high permeability from a mixed gascomposed of a plurality of components including ammonia gas, andhydrogen gas, and/or nitrogen gas even under high temperatureconditions, among various zeolite membranes, a zeolite membrane having asurface containing a specific molar ratio of nitrogen atoms to Al atomsneeds to be used, thereby completing the present invention. The secondembodiment (Invention B) of the present invention has been achievedbased on such findings, and provides the following.

[B1] A zeolite membrane, wherein a molar ratio of nitrogen atoms to Alatoms determined by X-ray photoelectron spectroscopy under the followingmeasurement conditions is from 0.01 to 4.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

[B2] The zeolite membrane according to [B1], wherein the zeolitemembrane is a zeolite membrane treated with an ammonium salt.[B3] The zeolite membrane according to [B2], wherein the zeolitemembrane is a zeolite membrane further treated with aluminum nitrate.[B4] The zeolite membrane according to any one of [B1] to [B3], whereinthe zeolite is RHO zeolite.[B5] The zeolite membrane according to any one of [B1] to [B4], whereinthe zeolite membrane is for ammonia gas separation.[B6] A method for separating ammonia, wherein ammonia gas is allowed topermeate and separated from a mixed gas containing at least ammonia gas,and hydrogen gas, and/or nitrogen gas by using the zeolite membraneaccording to any one of [B1] to [B5].[B7] The method for separating ammonia, wherein ammonia obtained in astep of producing ammonia from hydrogen gas and nitrogen gas isseparated by the separation method according to [B6].

In order to solve the above-described problems, the present inventorshave further studied separation of ammonia gas by using a zeolitemembrane, and found that although, regarding the separation performanceof existing zeolite membranes for ammonia gas separation that canseparate ammonia gas more selectively and efficiently than existingsilica membranes, the permeance ratio (ideal separation factor) ofammonia gas and nitrogen gas was only about 14 at most, and there is aproblem that the durability of such a zeolite membranes is impaired evenunder a relatively low temperature condition of 140° C., when a zeolitemembrane having a surface in which the molar ratio of Si atoms to Alatoms determined by X-ray photoelectron spectroscopy (XPS) is in aspecific range is used, significant ammonia separation performance isexhibited and the separation stability under high temperature conditionsis improved. Specifically, the present inventors have found that inorder to separate ammonia gas with high selectivity and highpermeability from a mixed gas composed of a plurality of componentsincluding ammonia gas and hydrogen gas and/or nitrogen gas even underhigh temperature conditions, among various zeolite membranes, a zeolitemembrane having a surface containing a specific molar ratio of Si atomsto Al atoms needs to be used, thereby completing the present invention.The third embodiment (Invention C) of the present invention has beenachieved based on such findings, and provides the following.

[C1] A zeolite membrane, wherein a molar ratio of Si atoms to Al atomsdetermined by using X-ray photoelectron spectroscopy under the followingmeasurement conditions is from 2.0 to 10.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

[C2] The zeolite membrane according to [C1], wherein the molar ratio ofnitrogen atoms to Al atoms determined by using X-ray photoelectronspectroscopy under the following measurement conditions is from 0.01 to4.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

[C3] The zeolite membrane according to [C1] or [C2], wherein the zeolitemembrane is a zeolite membrane treated with an aluminum salt.[C4] The zeolite membrane according to any one of [C1] to [C3], whereinthe zeolite membrane is a zeolite membrane treated with an ammoniumsalt.[C5] The zeolite membrane according to any one of [C1] to [C4], whereinthe zeolite membrane is a zeolite membrane treated with an aluminum saltafter being treated with an ammonium salt.[C6] The zeolite membrane according to any one of [C1] to [C5], whereinthe zeolite is RHO zeolite.[C7] The zeolite membrane according to any one of [C1] to [C6], whereinthe zeolite membrane is for ammonia separation.[C8] A method for separating ammonia, wherein ammonia gas is allowed topermeate and separated from a mixed gas containing at least ammonia gasand hydrogen gas and/or nitrogen gas by using the zeolite membraneaccording to any one of [C1] to [C7].[C9] A method for separating ammonia, wherein ammonia obtained in a stepof producing ammonia from hydrogen gas and nitrogen gas is separated bythe separation method according to [C8].

In order to solve the above-described problems, the present inventorshave further studied separation of ammonia gas by using a zeolitemembrane, and found that when a zeolite membrane having a surface inwhich the molar ratio of alkali metal atoms to Al atoms determined byX-ray photoelectron spectroscopy (XPS) is in a specific range is used,the permeation performance can be improved while maintaining highammonia gas separation selectivity. The present inventors have alsofound that the ammonia gas separation performance can be stablymaintained even under high temperature conditions by using the presentinvention. Specifically, the present inventors have found that in orderto separate ammonia gas with high selectivity and high permeability froma mixed gas composed of a plurality of components including ammonia gasand hydrogen gas and/or nitrogen gas even under high temperatureconditions, among various zeolite membranes, a zeolite membrane having asurface containing a specific molar ratio of alkali metal atoms to Alatoms needs to be used, thereby completing the present invention. Thefourth embodiment (Invention D) of the present invention has beenachieved based on such findings, and provides the following.

[D1] A zeolite membrane, wherein a molar ratio of alkali metal atoms toAl atoms determined by X-ray photoelectron spectroscopy under thefollowing measurement conditions is from 0.01 to 0.070.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

[D2] The zeolite membrane according to [D1], wherein the molar ratio ofnitrogen atoms to Al atoms determined by X-ray photoelectronspectroscopy under the following measurement conditions is from 0.01 to4.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

[D3] The zeolite membrane according to [D1] or [D2], wherein the zeolitemembrane is a zeolite membrane treated with an alkali metal salt.[D4] The zeolite membrane according to any one of [D1] to [D3], whereinthe zeolite membrane is a zeolite membrane treated with an ammoniumsalt.[D5] The zeolite membrane according to any one of [D1] to [D4], whereinthe zeolite membrane is a zeolite membrane treated with an alkali metalsalt after being treated with an ammonium salt.[D6] The zeolite membrane according to any one of [D1] to [D5], whereinthe zeolite is RHO zeolite.[D7] The zeolite membrane according to any one of [D1] to [D6], whereinthe zeolite membrane is for ammonia gas separation.[D8] A method for separating ammonia, wherein ammonia gas is allowed topermeate and separated from a mixed gas containing at least ammonia gasand hydrogen gas and/or nitrogen gas by using the zeolite membraneaccording to any one of [D1] to [D7].[D9] A method for separating ammonia, wherein ammonia obtained in a stepof producing ammonia from hydrogen gas and nitrogen gas is separated bythe separation method according to [D8].

In order to solve the above-described problems, the present inventorshave further studied separation of ammonia gas by using a zeolitemembrane composite, and found that although zeolite membranes canseparate ammonia gas more selectively and efficiently than existingsilica membranes, as described in Reference Example E1 of the presentinvention, when a zeolite membrane composite obtained by membraneformation of CHA zeolite as proposed in Patent Document 8 in which thechange rate of thermal contraction coefficient changes monotonously suchthat change rates of thermal contraction coefficient at 200° C. and 300°C. with respect to 30° C. are 0.13% and 0.30% (c-axis direction),respectively is used, there is room for improvement because the ammoniagas separation performance decreases particularly in the temperaturerange higher than 200° C. This is presumably because a crack occurs inthe grain boundary of zeolite due to thermal contraction, and gaspermeates through the crack. In contrast, the present inventors havefound that as in RHO zeolite described in Example E of the presentinvention, even in the case of zeolite with a change rate of thermalcontraction coefficient of 200° C. with respect to 30° C. of 1.55%,which considerably contracts compared with CHA zeolite, and exhibitsnon-linear thermal expansion/contraction behavior with respect totemperature, when the change rate of thermal expansion coefficient at300° C. is about 0.02%, ammonia can be efficiently and selectivelyseparated under high temperature conditions exceeding 200° C.

In other words, in order to solve one of the problems of the presentinvention which is to separate ammonia gas from a gas mixture composedof a plurality of components including ammonia gas, and hydrogen gas,and/or nitrogen gas with high selectivity and high permeability underhigh temperature conditions, the present inventors have found that amongvarious zeolite membrane composites, a zeolite membrane composite inwhich a zeolite exhibiting the change rate of a thermal expansioncoefficient in a specific temperature region is formed into a membraneneeds to be applied, thereby completing the present invention. Herein,the change rate of the thermal expansion coefficient is the change rateof the thermal expansion coefficient in the axial direction where thechange rate of the thermal expansion coefficient is maximized. Forexample, CHA zeolite has different thermal expansion/contraction ratesin the a-axis and c-axis directions, and the change rate is larger inthe c-axis. Therefore, the change rate of thermal expansion coefficientof CHA is the change rate of thermal expansion coefficient in the c-axisdirection. Similarly, MFI zeolite has different thermalexpansion/contraction rates in the a-axis, b-axis, and c-axisdirections, and the change rate is larger in the c-axis. Therefore, thechange rate of thermal expansion coefficient of MFI herein is the changerate of thermal expansion coefficient in the c-axis direction. On theother hand, RHO zeolite is cubic and all crystal axes are equivalent,and therefore the change rate of thermal expansion coefficient isconstant regardless of the axial direction. The fifth embodiment(Invention E) of the present invention has been achieved based on suchfindings, and provides the following.

[E1] A zeolite membrane composite for ammonia separation containingzeolite, wherein a change rate of a thermal expansion coefficient at300° C. with respect to a thermal expansion coefficient at 30° C. of thezeolite is equal to or within ±0.25% and a change rate of a thermalexpansion coefficient at 400° C. with respect to the thermal expansioncoefficient at 30° C. of the zeolite is equal to or within ±0.35%.[E2] The zeolite membrane composite for ammonia separation according to[E1], wherein the change rate of the thermal expansion coefficient at400° C. with respect to the thermal expansion coefficient at 30° C. ofthe zeolite with respect to the change rate of the thermal expansioncoefficient at 300° C. with respect to the thermal expansion coefficientat 30° C. of the zeolite is equal to or within ±120%.[E3] The zeolite membrane composite for ammonia separation according to[E1] or [E2], wherein the zeolite is RHO zeolite or MFI zeolite.[E4] The zeolite membrane composite for ammonia separation according toany one of [E1] to [E3], wherein the zeolite has an SiO₂/Al₂O₃ molarratio of from 6 to 500.[E5] A method for separating ammonia, wherein ammonia is separated froma gas mixture containing at least ammonia gas, and hydrogen gas, and/ornitrogen gas by using the zeolite membrane composite for separatingammonia gas according to any one of [E1] to [E4].[E6] A method for separating ammonia, wherein ammonia obtained in a stepof producing ammonia from hydrogen gas and nitrogen gas is separated bythe separation method according to [E5].

The second to fifth embodiments are techniques related to an ammonia gasseparation membrane that contributes to completion of an energy-savingproduction process of ammonia, and are techniques that can be expectedto be applied to a reaction-separation-type ammonia production processwhich is one embodiment of the present invention.

Advantageous Effects of Invention

According to the first embodiment of the present invention, ammonia gascan be separated from a mixed gas composed of a plurality of componentsincluding ammonia gas, hydrogen gas, and nitrogen gas to the permeationside continuously and efficiency with high selectivity. Since the methodof the present invention can be used stably even under high temperatureconditions exceeding 50° C. and even 200° C., the ammonia gaspermeability is high. As a result, the membrane area required forseparation can be reduced, and ammonia separation can be performed at alow cost with a small-scale facility.

Specific examples of application of the zeolite membrane of the presentinvention include an ammonia production process as typified by theHaber-Bosch process, and in this process, when recovering ammonia from amixed gas composed of a plurality of components including ammonia gasand hydrogen gas and nitrogen gas recovered from a reactor, ammonia canbe separated more efficiently than conventional cold condensationseparation method, and therefore, the cooling energy for ammoniacondensation can be reduced.

In another aspect, the zeolite membrane of the present invention canstably separate ammonia gas from a mixed gas composed of a plurality ofcomponents including ammonia gas, hydrogen gas, and nitrogen gas to thepermeation side with high permeability, even under high temperatureconditions, a reaction-separation-type ammonia production process inwhich the zeolite membrane of the present invention is installed in areactor, and ammonia gas generated is recovered at the same time whileammonia gas is generated can be designed.

According to the second to fifth embodiments of the present invention,even under high temperature conditions, ammonia gas can be separatedcontinuously from a mixed gas composed of a plurality of componentsincluding ammonia gas, and hydrogen gas, and/or nitrogen gas to thepermeation side stably and efficiently with high selectivity. Since thezeolite membrane of the present invention can be used stably even underhigher temperature conditions, the ammonia gas permeability is high. Asa result, the membrane area required for separation can be reduced, andammonia gas separation can be performed at a low cost with a small-scalefacility.

Specific examples of application of the zeolite membrane of the presentinvention include an ammonia production process represented by theHaber-Bosch process, and in this process, when recovering ammonia from amixed gas composed of a plurality of components including ammonia gasand hydrogen gas and/or nitrogen gas recovered from a reactor, ammoniacan be separated more efficiently than conventional cold condensationseparation method, and therefore, the cooling energy for ammoniacondensation can be reduced.

In another aspect, the zeolite membrane of the present invention canstably separate ammonia gas from a mixed gas composed of a plurality ofcomponents including ammonia gas, and hydrogen gas, and/or nitrogen gasto the permeation side with high permeability, even under hightemperature conditions, a reaction-separation-type ammonia productionprocess in which the zeolite membrane of the present invention isinstalled in a reactor, and ammonia gas generated at the same time isrecovered while ammonia gas is generated can be designed.

In particular, when the first to fifth embodiments are applied to areaction-separation-type ammonia production process, not only reductionof reaction pressure during ammonia production is expected but alsoconsiderable improvement in conversion rate of raw material gas toammonia gas and reduction of the amount of recovered gas recycled to areactor during production can be expected. In other words, areaction-separation-type ammonia production process employing thezeolite membrane of the present invention enables suppression of energyconsumption during production, and energy-saving ammonia production alsoexcellent in economical efficiency.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic diagram showing a configuration of an apparatusused in an ammonia gas separation test in Examples.

FIG. 2 is a measurement result of thermal expansion coefficients of thezeolite according to Example E4 for respective temperatures.

DESCRIPTION OF EMBODIMENTS

Hereinafter, although the embodiment of the present invention will bedescribed in more detail, the description of the constituent elementsdescribed below is an example of the embodiment of the presentinvention, and the present invention is not limited thereto. Variousmodifications can be made within the scope of the present invention. Thezeolite herein is a zeolite defined by the International ZeoliteAssociation (IZA). The structure is characterized by X-ray diffractiondata. Herein, “porous support-zeolite membrane composite in which azeolite membrane is formed on a porous support” may be referred to as“zeolite membrane composite” or “membrane composite”. “Porous support”may be simply abbreviated as “support”, and “aluminosilicate zeolite” issometimes simply referred to as “zeolite”. Furthermore, herein,“hydrogen gas”, “nitrogen gas”, and “ammonia gas” may be simply referredto as “hydrogen”, “nitrogen”, and “ammonia”, respectively. On the otherhand, ammonia separation in the present invention means obtaining amixed gas containing a higher concentration of ammonia gas from a mixedgas containing ammonia gas.

The first embodiment of the ammonia separation method of the presentinvention (Invention A) is a method for stable and continuous separationof ammonia from a mixed gas composed of a plurality of componentsincluding at least ammonia, hydrogen, and nitrogen to the permeationside with high permeability and high selectivity using a zeolitemembrane, and is characterized in that ammonia is selectively allowed topermeate and separated from a mixed gas of hydrogen and nitrogencontaining a specific amount of ammonia.

Another embodiment of the method for separating ammonia of the presentinvention is characterized in that a mixed gas composed of a pluralityof components including ammonia and hydrogen and/or nitrogen is broughtinto contact with a specific zeolite membrane, and ammonia isselectively allowed to permeate and separated from the mixed gas.

Details will be described below.

<Method for Producing Ammonia>

Since the ammonia separation method according to the present embodimentcan be used effectively when efficiently separating ammonia from a mixedgas containing at least ammonia, hydrogen, and nitrogen, it is effectiveto use the method in combination with a method for producing ammoniafrom which such a mixed gas can be obtained. Specifically, in additionto a method for producing ammonia, including a first step of producingammonia from hydrogen and nitrogen and a second step of separatingammonia obtained in the first step by the ammonia separation methoddescribed below, wherein ammonia obtained in the first step is separatedin the second step, a method for producing ammonia, wherein the firststep and the second step proceed in one reactor is also a preferredembodiment of the present invention. That the first step and the secondstep proceed in one reactor means that the first step and the secondstep proceed simultaneously. In other words, in one embodiment of thepresent invention, ammonia gas can be produced from hydrogen gas andnitrogen gas in a container, and ammonia can be efficiently producedwhile separating ammonia from a mixed gas containing ammonia gasproduced in the container.

There is no particular limitation on the industrial production method ofammonia, and examples thereof include the Haber-Bosch process. In thismethod, a process in which iron oxide is basically used as a catalyst,and ammonia is produced by reacting nitrogen gas and hydrogen gas on thecatalyst at a high temperature and high pressure of from 300 to 500° C.and from 10 to 40 MPa, and while produced ammonia contained in gas at anoutlet of a reactor is cooled and condensed and recovered as a product,and unreacted nitrogen and hydrogen gas is separated and recycled as rawmaterial gas is adopted. As an improved method of the Haber-Boschprocess, a Ru-based supported catalyst capable of producing ammoniaunder a lower pressure condition was developed in the 1980s, and while aprocess combined with the Haber-Bosch process has been industrialized,the basic production process has not changed for 100 years. As describedabove, industrial catalysts for ammonia production are generally roughlyclassified into iron-based catalysts and Ru-based catalysts. Althoughthe molar ratio of raw material gas used in production of ammonia ispreferably a theoretical ratio of hydrogen/nitrogen=3, since Ru-basedcatalysts are likely to be poisoned by hydrogen, production conditionswith a reduced molar ratio of hydrogen/nitrogen are preferably used. Inview of this, a catalytic process of ammonia production combined withthe ammonia separation technique of the present invention is notparticularly limited, and since a value close to a preferable volumeratio of hydrogen gas/nitrogen gas contained in a supply gas in theammonia separation described below can be obtained, a process using aRu-based catalyst is preferable, and this combination can reduce thehydrogen permeation amount in separation of ammonia to be produced.

<Method for Separating Ammonia>

The first embodiment of the method for separating ammonia of the presentinvention is characterized in that, using a zeolite membrane, a mixedgas composed of a plurality of components including ammonia, hydrogen,and nitrogen is brought into contact with the zeolite membrane, andammonia is selectively permeated and separated from the mixed gas.

The method for separating ammonia of the present invention ischaracterized in that, using a specific zeolite membrane, a mixed gascomposed of a plurality of components including ammonia, hydrogen,and/or nitrogen is brought into contact with the zeolite membrane, andammonia is selectively permeated and separated from the mixed gas.

As described above, according to the present invention, ammonia gas canbe produced from hydrogen gas and nitrogen gas in a reactor, and ammoniacan be efficiently produced and recovered in the reactor while allowingproduced ammonia gas to permeate using a zeolite membrane.

Ammonia separation by the zeolite membrane in the present invention ismainly based on the hopping mechanism of ammonia in zeolite pores, andalso utilizes a molecular sieve by controlling the pore diameter of thezeolite membrane by adsorbed ammonia, ammonium ions, or the like. By theformer action, ammonia having high affinity with the zeolite membranecan permeate the zeolite membrane with high selectivity, and since thelatter action efficiently separates gas molecules having the size of theeffective pore diameter of an ammonia-adsorbed zeolite membrane or moreand gas molecules having the size of less than that, ammonia can be moreeffectively separated.

Although factors of considerable improvement in the ammonia permeationselectivity by a hopping mechanism of ammonia in zeolite pores are notyet known in detail, such an improvement is due to the fact that thepore diameter in the zeolite membrane is narrowed by adsorbed ammoniaand ammonium ions contained in zeolite, and therefore the permeationamount of hydrogen gas having a particularly small molecular size can bereduced. Since this action narrows pores of the zeolite membrane in thesame manner even when zeolite having a pore diameter larger than themolecular size of hydrogen gas, nitrogen gas, or ammonia gas is used,inhibition of permeation of nitrogen gas or hydrogen gas appears. On theother hand, adsorbed ammonia and ammonium ions contained in the zeolitepores can cause hopping movement by adsorption/desorption of ammonia inthe pores, and this behavior causes selective separation of ammonia gas.

The first embodiment of the present invention (Invention A) ischaracterized by separating ammonia based on the hopping mechanism ofammonia in the zeolite pores by utilizing adsorption of ammonia tozeolite as described above, and therefore, the ammonia gas concentrationin a supply gas containing hydrogen gas, nitrogen gas, and ammonia gasneeds to be controlled to a specific amount or more. The concentrationis important to be 1.0% by volume or more as the concentration ofammonia gas in a supply gas. This is because ammonia adsorbed on zeoliteand ammonia gas is in an adsorption equilibrium relationship withammonia gas in a gas phase, and the adsorption ability of ammonia to thezeolite greatly depends on the ammonia gas concentration in the supplygas. As shown in Comparative Examples of the present invention, evenwhen the ammonia gas concentration is less than 1.0% by volume, someammonia permeation selectivity is exhibited, but the effect is notconsiderable. Therefore, in the present invention, it is important touse a supply gas having an ammonia gas concentration of 1.0% by volumeor more, and when such a gas is brought into contact with a zeolitemembrane under a pressurized condition, adsorption of ammonia to zeolitecan be effectively caused, and the ammonia separation selectivity fromthe supply gas can be improved. In addition, when a supply gas having anammonia gas concentration of 1.0% by volume or more is used, the ammoniagas concentration in the supply gas is improved, and therefore, thepermeation amount is also improved. When the ammonia gas concentrationin the mixed gas is 1.0% by volume or more, ammonia may be producedunder conditions such that the ammonia gas concentration in the mixedgas obtained when producing ammonia is 1.0% by volume or more. Among theabove, the ammonia gas concentration in the supply gas is preferably2.0% by volume or more, more preferably 3.0% by volume or more, andparticularly preferably 5.0% by volume or more. On the other hand, theupper limit of the ammonia gas concentration in the supply gas is notparticularly limited, and is usually less than 100% by volume since theseparation performance is improved as the concentration is higher, andbecause of the need to separate ammonia, the ammonia gas concentrationis generally 80% by volume or less, preferably 60% by volume or less,and more preferably 40% by volume or less. The ammonia concentration interms of % by volume in the supply gas is considered to correspond tothe molar fraction of ammonia obtained by collecting the supply gas andanalyzing the components. Similarly, the concentration of another gas interms of % by volume is also considered to correspond to the molarfraction of the gas. On the other hand, when ammonia is separated incombination with an ammonia production process, the ammoniaconcentration is equal to or less than the equilibrium concentration ofammonia produced under production process conditions of the productionprocess. In contrast to a known method for selectively allowing hydrogengas and/or nitrogen gas in a mixed gas of hydrogen, nitrogen, andammonia to permeate, the ammonia separation technique using the presentinvention is a process for separating ammonia from a supply gas, andtherefore, ammonia separation from a mixed gas containing a highconcentration of ammonia is advantageous. Even when, if necessary,adopting a step of recovering hydrogen gas from a mixed gas on thenon-permeation side that did not permeate the membrane after theseparation, the above-described problems in a known process ofconcentrating ammonia by separating hydrogen and/or nitrogen from asupply gas are less likely to occur due to the design of recoveringhydrogen from the mixed gas whose ammonia gas concentration issufficiently lowered. For example, the separation technique of thepresent invention is characterized by considerably improving ammoniaseparation performance and high separation stability duringhigh-temperature operation or long-term operation as compared withPatent Document 7.

As described above, although factors of considerable improvement in theammonia permeation selectivity that permeates the zeolite membrane whenthe ammonia gas concentration in the mixed gas of hydrogen, nitrogen,and ammonia is a specific amount or more are not yet known in detail,when the ammonia gas concentration in the mixed gas is increased,adsorption to zeolite is likely to occur due to the adsorptionequilibrium between ammonia gas and zeolite, and a zeolite membrane inwhich ammonia is adsorbed in pores is first generated. Since anammonia-adsorbed zeolite membrane produced in this way narrows the porediameter in the zeolite membrane, the permeation amount of hydrogen witha small molecular size can be reduced. Since this action narrows thepores of the zeolite membrane in the same manner even when zeolitehaving a pore diameter larger than the molecular sizes of hydrogen,nitrogen, and ammonia is used, hydrogen permeation inhibition isconsiderably exhibited. On the other hand, ammonia adsorbed in thezeolite pores can cause hopping movement by adsorption/desorption ofammonia in pores due to the pressure difference between the inside andoutside of the membrane, and this behavior causes selective separationof ammonia.

In other words, the present invention is a technique that firstaggressively adsorbs ammonia on zeolite to control the pore diameter ofa zeolite membrane to increase the ammonia separation selectivity whileselectively allowing ammonia to permeate using hopping movement byadsorption/desorption of ammonia in pores. In contrast, Patent Document8 is greatly different from the present invention in that a technique todesign zeolite that does not cause such adsorption and to separateammonia by molecular sieve using the pore diameter of zeolite isproposed since such an ammonia-adsorbed zeolite membrane causes cloggingin ammonia permeation. On the other hand, the silica film as proposed inPatent Document 7 hardly adsorbs ammonia, and even when ammonia isadsorbed, the heat stability is low, and therefore, an effect of thepresent invention is not exhibited.

On the other hand, in the present invention in which ammonia isseparated mainly by utilizing a hopping mechanism in pores accompaniedby adsorption/desorption of ammonia to zeolite, the ammonia separationtemperature is one of important design factors since the temperaturegreatly affects the long-term durability of a zeolite membrane used, theammonia separation performance of a zeolite membrane, and the productionenergy balance of the entire process when combined with ammoniaproduction facilities. From these viewpoints, in the present invention,when separating a product gas in ammonia synthesis, the temperatureduring ammonia separation is usually the same as or lower than thesynthesis temperature of ammonia, and the temperature during ammoniaseparation is the temperature in a separator that performs ammoniaseparation, or the temperature of a mixed gas used for the separation orthe temperature of the separated ammonia gas. The temperature of aseparation membrane can be regarded as almost the same as thetemperature in a separator. From the design of an ammonia productionprocess, it is preferable to perform separation at the same temperatureas the synthesis temperature since it is not necessary to raise thetemperature of hydrogen and nitrogen to be recycled to a reactor. Forthis reason, although a preferable temperature in the case of ammoniaseparation depends on the reaction temperature in an ammonia synthesisreaction, the temperature is usually 500° C. or lower, preferably 450°C. or lower, and more preferably 400° C. or lower. When ammonia isseparated under these temperature conditions using the zeolite membraneof the present invention, not only continuous operation over a longperiod of time is possible, but also high ammonia permeation selectivityis exhibited since the zeolite membrane has high stability. On the otherhand, the lower limit is usually a temperature higher than 50° C.,preferably 100° C. or higher, more preferably 150° C. or higher, furtherpreferably 200° C. or higher, especially preferably 250° C. or higher,and particularly preferably 300° C. or higher. When ammonia is separatedunder these temperature conditions, the desorption rate of ammoniaadsorbed in zeolite pores is improved, and as a result, the ammoniapermeation amount of a zeolite membrane is improved. When a raw materialgas is recycled in an ammonia production process, ammonia separationunder a higher temperature condition is preferable since energy requiredto raise the temperature of hydrogen and nitrogen is reduced, and fromthis viewpoint, the lower limit of the temperature is preferably 250° C.or higher, and more preferably 300° C. or higher.

In the method for separating ammonia by hopping movement in pores as inthe present invention, the rate can be controlled by controlling themolar ratio of alkali metal atoms to Al atoms in zeolite pores to beless than the saturation amount ratio, and as a result, control of themolar ratio is important and may be preferred in combination with amethod for controlling the molar ratio to from 0.01 to 0.070 as in thefourth embodiment of the present invention.

The composition of another gas in a supply gas (mixed gas) is notparticularly limited, and the volume ratio of hydrogen gas/nitrogen gascontained in the supply gas is usually 3 or less, and more preferably 2or less. By adjusting to this volume ratio, the permeation amount ofhydrogen during ammonia separation is reduced, and the ammoniaseparation selectivity is improved. For this reason, when a supply gasof the ammonia separation process of the present invention is obtainedfrom an ammonia production process, although not particularly limitedthereto, it is preferable to combine with a Ru-based catalytic processof ammonia production with a low volume ratio of hydrogen gas/nitrogengas in raw material gas. On the other hand, since the smaller the lowerlimit, the better the ammonia separation selectivity, the lower limit isnot particularly limited, and is usually 0.2 or more, preferably 0.3 ormore, and more preferably 0.5 or more. Here, the upper limit and lowerlimit values are valid within the range of significant figures, andspecifically, the upper limit of 3 or less means from 2.5 to less than3.5, while 0.2 or more means from 0.15 to less than 0.25, and 1.0 ormore means from 0.95 to less than 1.05.

In a preferred aspect of the present invention, the higher the pressureof a supply gas (mixed gas), the more the separation performance of azeolite membrane is improved, and the area of the zeolite membrane to beused can be reduced. The pressure is not particularly limited as long asthe pressure is equal to or higher than atmospheric pressure, and amembrane may be used at a desired pressure by appropriately adjustingthe pressure. When the pressure of gas to be separated is lower than thepressure used for separation, the gas can be used by increasing thepressure with a compressor or the like.

The pressure of a supply gas is usually atmospheric pressure or higherthan atmospheric pressure, and preferably 0.1 MPa or more, and morepreferably 0.2 MPa or more. The upper limit value is usually 20 MPa orless, and preferably 10 MPa or less, and more preferably 5 MPa or less,and may be 3 MPa or less.

The pressure on the permeation side is not particularly limited as longas the pressure is lower than the pressure of gas on the supply side,and is usually 10 MPa or less, preferably 5 MPa or less, more preferably1 MPa or less, and further preferably 0.5 MPa or less, and in somecases, the pressure may be lowered to a pressure of atmospheric pressureor less. When separating until the ammonia concentration in a supply gasis low, the permeation side is preferably at a low pressure, and whenthe pressure is reduced to a pressure below atmospheric pressure,ammonia can be separated until the ammonia gas concentration in thesupply gas becomes lower.

The differential pressure between gas on the supply side and gas on thepermeation side is not particularly limited, and is usually 20 MPa orless, preferably 10 MPa or less, more preferably 5 MPa or less, andstill more preferably 1 MPa or less. The differential pressure isusually 0.001 MPa or more, and preferably 0.01 MPa or more, and morepreferably 0.02 MPa or more.

Here, the differential pressure refers to the difference between thepartial pressure on the gas supply side and the partial pressure on thepermeation side. The pressure [Pa] indicates an absolute pressure unlessotherwise specified.

The flow rate of a supply gas is such that can compensate for thedecrease due to permeating gas, and the flow rate may be such that thesupply gas can be mixed in such a manner that the concentration of gasin the vicinity of gas with a low permeability in the supply gas matchesthe concentration in the entire gas, and, depending on the tube diameterof the zeolite membrane composite and the separation performance of themembrane, the flow rate as the linear velocity is usually 0.001 mm/secor more, and preferably 0.01 mm/sec or more, more preferably 0.1 mm/secor more, still more preferably 0.5 mm/sec or more, and especiallypreferably 1 mm/sec or more, and the upper limit is not particularlylimited, and is usually 1 m/sec or less, and preferably 0.5 m/sec orless.

In the method for separating ammonia from a mixed gas of the presentinvention, a sweep gas may be used. The sweep gas means gas supplied toefficiently recover ammonia permeated through a separation membrane, andis gas supplied to the permeation side of the separation membrane, notgas introduced to the supply gas side before separation permeation.Specifically, the sweep gas is gas supplied separately from the supplygas before separation and permeation, and gas of a different kind fromthe supply gas is allowed to flow on the permeation side to recover thegas that has permeated through the membrane. The sweep gas used in thepresent invention refers to, for example, gas 9 supplied from a line 12shown in FIG. 1. The pressure of the sweep gas is usually atmosphericpressure, and is not particularly limited to atmospheric pressure, andpreferably 20 MPa or less, more preferably 10 MPa or less, and stillmore preferably 1 MPa or less, and the lower limit is preferably 0.09MPa or more, and more preferably 0.1 MPa or more. In some cases, thepressure may be reduced.

The flow rate of the sweep gas is not particularly limited, and the flowrate as the linear velocity is usually 0.5 mm/sec or more, andpreferably 1 mm/sec or more, and the upper limit is not particularlylimited, and is usually 1 m/sec or less, and preferably 0.5 m/sec orless.

An apparatus used for gas separation is not particularly limited, andusually a zeolite membrane composite made into a membrane module is used(hereinafter, “zeolite membrane composite and/or separation apparatususing zeolite membrane composite” may be simply referred to as “membranemodule”). The membrane module may be, for example, an apparatus asschematically shown in FIG. 1, and for example, a membrane moduleexemplified in “Gas Separation/Purification Technology”, TORAY ResearchCenter, Inc, 2007, page 22, and the like may be used.

A separation operation of a mixed gas in the apparatus of FIG. 1 will bedescribed in a section of Examples.

When performing membrane separation of ammonia from a mixed gas,membrane modules may be used in multiple stages. In this case, gas forseparation may be supplied to the first-stage membrane module, and thenon-permeation side gas that has not permeated the membrane may besupplied to the second-stage membrane module, or the permeated gas maybe supplied to the second-stage membrane module. In the former method,the concentration of a low permeable component on the non-permeationside can be further increased, and in the latter method, theconcentration of a highly permeable component in the permeated gas canbe further increased. A method combining these methods can also besuitably used.

When separation is performed by membrane modules provided in multiplestages, the pressure of a supply gas may be adjusted with a booster orthe like as necessary when supplying gas to a subsequent membranemodule.

When membrane modules are used in multiple stages, membranes havingdifferent performance may be installed in each stage. In general,regarding membrane performance, a membrane having high permeationperformance has low separation performance, while a membrane having highseparation performance tends to have low permeation performance. Forthis reason, when processing until a gas component to be separated orconcentrated reaches a predetermined concentration, while a membranehaving high permeability reduces a required membrane area, a lowpermeable component is likely to be permeated to the permeation side,and therefore, the concentration of a highly permeable component in thepermeation side gas tends to be low. Conversely, in a membrane with highseparation performance, permeation of a low permeable component to thepermeation side is unlikely to occur, and for this reason, although theconcentration of a highly permeable component in the permeation side gasis high, a required membrane area tends to become large. While it isdifficult to control the relationship between the required membrane areaand the permeation or non-permeation amount of gas for concentration orseparation by separation with one kind of membrane, it is easy tocontrol the relationship when membranes with different performances areused. Depending on the membrane cost and the price of gas to beseparated or recovered, a membrane can be installed in such a mannerthat an optimum relationship between the membrane area and thepermeation or non-permeation amount of gas for concentration orseparation can be obtained, and the overall merit can be maximized.

For example, when ammonia cannot be sufficiently separated by one-stagemembrane separation, the non-permeation side gas can be furtherseparated by several stages of membranes. In the case of one-stagemembrane separation, the separation of ammonia/hydrogen in the membraneis not sufficient, and when a lot of hydrogen is contained on thepermeation side together with ammonia, it is also possible to separatethe permeated gas with a membrane having high separation performance ofammonia and hydrogen.

The zeolite membrane used in the present invention has excellentchemical resistance, oxidation resistance, heat stability, and pressureresistance, and exhibits high ammonia permeation performance andseparation performance, and excellent durability.

The high permeation performance herein indicates a sufficientthroughput, and for example, when ammonia is permeated at a temperatureof 200° C. and a differential pressure of 0.3 MPa, for example, thepermeance of a gas component that permeates a membrane [mol/(m²·s·Pa)]is usually 1×10⁻⁹ or more, and preferably 5×10⁻⁹ or more, morepreferably 1×10⁻⁸ or more, still more preferably 2×10⁻⁸ or more,especially preferably 5×10⁻⁸ or more, particularly preferably 1×10⁻⁷ ormore, and most preferably 2×10⁻⁷ or more. The upper limit is notparticularly limited, and is usually 3×10⁻⁴ or less.

The permeance [mol/(m²·s·Pa)] of the zeolite membrane composite used inthe present invention is, for example, when nitrogen is permeated underthe same conditions, usually 5×10⁻⁸ or less, preferably 3×10⁻⁸ or less,more preferably 1×10⁻⁸ or less, particularly preferably 5×10⁻⁹ or less,and most preferably 1×10⁻⁹ or less, and ideally, the permeance is 0, andmay be on the order of from 1×10⁻¹⁰ to 1×10⁻¹⁴ in practice.

Herein, the permeance (also referred to as “permeability”) is obtainedby dividing the amount of permeated substance by the product of themembrane area, time, and the partial pressure difference between thesupply side and the permeation side of the permeated substance, the unitthereof is [mol/(m²·s·Pa)], and the value thereof is a value calculatedby the method described in a section of Examples.

The selectivity of a zeolite membrane is expressed by an idealseparation factor and a separation factor. The ideal separation factorand the separation factor are indicators that represent the selectivitygenerally used in membrane separation, and the ideal separation factoris a value calculated by the method described in a section of Examples,and the separation factor is a value calculated as follows.

When obtaining the separation coefficient α, the following formula isused.

α=(Q′1/Q′2)/(P′1/P′2)

[In the above formula, Q′1 and Q′2 indicate the permeation amount of ahighly permeable gas and the permeation amount of a low permeable gas[mol/(m²·s·Pa)], respectively, and P′1 and P′2 indicate partialpressures [Pa] of the highly permeable gas and the low permeable gas ina supply gas, respectively.]

The separation factor α can also be obtained as follows.

α=(C′1/C′2)/(C1/C2)

[In the above formula, C′1 and C′2 indicate the concentration of ahighly permeable gas and the concentration of a low permeable gas [% byvolume] in the permeated gas, and C1 and C2 indicate the concentrationof the highly permeable gas and the concentration of the low permeablegas [% by volume] in a supply gas, respectively.]

The ideal separation factor is, for example, when ammonia and nitrogenare permeated at a temperature of 200° C. and a differential pressure of0.3 MPa, usually 15 or more, and preferably 20 or more, more preferably25 or more, and most preferably 30 or more. The ideal separation factoris, when ammonia and hydrogen are permeated at a temperature of 200° C.and a differential pressure of 0.3 MPa, usually 2 or more, andpreferably 3 or more, more preferably 5 or more, still more preferably 7or more, especially preferably 8 or more, particularly preferably 10 ormore, and most preferably 15 or more. The upper limit of the idealseparation factor is in a case where only ammonia is completelypermeated, and in this case, the upper limit is infinite, and inpractice, the separation factor may be about 100,000 or less.

The separation factor of the zeolite membrane used in the presentinvention is for example, when a mixed gas of 1:1 volume ratio ofammonia and nitrogen is permeated at a temperature of 50° C. and adifferential pressure of 0.1 MPa, usually 2 or more, and preferably 3 ormore, more preferably 4 or more, and further preferably 5 or more. Theupper limit of the separation factor is in a case where only ammonia iscompletely permeated, and in this case, the separation factor isinfinite, and in practice, the separation factor may be about 100,000 orless.

The zeolite membrane used in the present invention, as described above,is excellent in chemical resistance, oxidation resistance, heatstability, pressure resistance, and exhibits high permeationperformance, separation performance, and is excellent in durability, andthe ammonia separation method of the present invention using such azeolite membrane can be applied to separation of ammonia from a productof ammonia synthesis. The method for separating ammonia of the presentinvention can also be utilized as a membrane reactor in which a zeolitemembrane is installed in an ammonia synthesis reactor and ammonia isselectively permeated and separated in the reactor to shift theequilibrium of hydrogen gas, nitrogen gas, and ammonia gas in a reactionsystem and efficiently synthesize ammonia at a high conversion rate.

(Zeolite)

In the present invention, zeolite constituting a zeolite membrane is analuminosilicate. An aluminosilicate is composed mainly of Si and Aloxides, and may contain another element as long as an effect of thepresent invention is not impaired. A cationic species contained in thezeolite of the present invention is preferably a cationic species thateasily coordinates to an ion exchange site of the zeolite, such as acationic species selected from the group of elements of group 1, group2, group 8, group 9, group 10, group 11, and group 12 of the periodictable, NH₄ ⁺, and two or more cationic species thereof, and morepreferably a cationic species selected from the group 1 and group 2elements of the periodic table, NH₄ ⁺, and two or more cationic speciesthereof.

The zeolite used in the present invention is an aluminosilicate. TheSiO₂/Al₂O₃ molar ratio of the aluminosilicate is not particularlylimited, and is usually 6 or more, preferably 7 or more, and morepreferably 8 or more, and the molar ratio is usually 500 or less, andpreferably 100 or less, more preferably 80 or less, still morepreferably, 50 or less, especially preferably 45 or less, particularlypreferably 30 or less, and most preferably 25 or less. Use of zeolitehaving such a specific region SiO₂/Al₂O₃ molar ratio is preferablebecause the denseness of a zeolite membrane and durability such aschemical reaction resistance and heat resistance can be improved. Fromthe viewpoint of the separation performance that allows ammonia in amixed gas composed of a plurality of components including ammonia,hydrogen, and nitrogen to permeate, from a reason that an acid site ofAl element becomes an adsorption site of ammonia as described above, itis preferable to use a zeolite containing more Al, and by using zeolitehaving the above-described SiO₂/Al₂O₃ molar ratio, ammonia can beseparated with high permeability and high selectivity.

The SiO₂/Al₂O₃ molar ratio of zeolite can be adjusted by the reactionconditions of hydrothermal synthesis described below.

Herein, the SiO₂/Al₂O₃ molar ratio is a numerical value determined byscanning electron microscope-energy dispersive X-ray spectroscopy(SEM-EDX). In this case, in order to obtain information only on amembrane having a thickness of several microns, measurement is usuallyperformed with an X-ray acceleration voltage of 10 kV.

Examples of the structure of the zeolite used in the present inventioneach represented by a code defined by the International ZeoliteAssociation (IZA) include ABW, ACO, AEI, AEN, AFI, AFT, AFX, ANA, ATN,ATT, ATV, AWO, AWW, BIK, CHA, DDR, DFT, EAB, EPI, ERI, ESV, GIS, GOO,ITE, JBW, KFI, LEV, LTA, MER, MON, MTF, OWE, PAU, PHI, RHO, RTE, RWR,SAS, SAT, SAV, SIV, TSC, UFI, VNI, YUG, AEL, AFO, AHT, DAC, FER, HEU,IMF, ITH, MEL, MFS, MWW, OBW, RRO, SFG, STI, SZR, TER, TON, TUN, WEI,MFI, MON, PAU, PHI, MOR, and FAU.

Among them, preferred is zeolite having a framework density of 18.0T/nm³ or less, more preferred is AEI, AFX, CHA, DDR, ERI, LEV, RHO, MOR,MFI, or FAU, still preferred is AEI, CHA, DDR, RHO, MOR, MFI, or FAU,particularly preferred is CHA, RHO, or MFI, and most preferred is RHO orMFI. When there are permeation components other than ammonia in a mixedgas containing ammonia by using zeolite with a low framework density,the resistance at the time of permeation of those permeation componentscan be reduced, and the permeation amount of ammonia can be easilyincreased.

In the fifth embodiment of the present invention (zeolite membranecomposite E), preferred is a zeolite having a framework density of 18.0T/nm³ or less, more preferred is AFX, DDR, ERI, LEV, RHO, MOR, MFI, orFAU, still more preferred is DDR, RHO, MOR, MFI, or FAU, and mostpreferred is RHO or MFI.

Here, the framework density (unit: T/nm³) means the number of T atoms(atoms other than oxygen among the atoms constituting the skeleton ofzeolite) present per unit volume (1 nm³) of zeolite, and this value isdetermined by the structure of zeolite. The relationship between theframework density and the structure of zeolite is shown in ATLAS OFZEOLITE FRAMEWORK TYPES Sixth Revised Edition 2007 ELSEVIER.

The membrane separation of ammonia and hydrogen and nitrogen of thepresent invention is characterized by ammonia separation based on ahopping mechanism of ammonia in a zeolite pore, utilizing adsorption ofammonia to zeolite, and although there is no particular limitation,zeolite having a pore diameter close to the molecular diameter ofammonia may be preferable because ammonia separation selectivity isimproved. From this point of view, the zeolite structure preferably hasan oxygen 8-membered ring pore. On the other hand, although a porehaving a size larger than that of oxygen 8-membered ring is preferablein that the ammonia permeability is high, the separation performancefrom hydrogen and/or nitrogen may be lowered. However, in the case ofusing a zeolite having a pore having a size larger than that of anoxygen 8-membered ring, when zeolite having a reduced SiO₂/Al₂O₃ molarratio is used, ammonia can be separated with high permeability and highselectivity since the pore diameter of the zeolite membrane iscontrolled by ammonia adsorbed on the Al site.

Accordingly, the effective pore diameter of zeolite used for membraneseparation greatly affects the pore diameter of a zeolite membrane towhich ammonia has been adsorbed, and thus is an important design factor.The effective pore diameter of zeolite can also be controlled by a metalspecies introduced into the zeolite, ion exchange, an acid treatment, asilylation treatment, and the like. It is also possible to improve theseparation performance by controlling the effective pore diameter byanother method.

For example, the pore diameter of zeolite is slightly affected by theatomic diameter of a metal species introduced into the zeoliteframework. When a metal having an atomic diameter smaller than that ofsilicon, specifically, such as boron (B) is introduced, the porediameter is reduced, and when a metal having an atomic diameter largerthan that of silicon, specifically, such as tin (Sn) is introduced, thepore diameter is increased. The pore diameter may be affected bydesorbing a metal introduced into the zeolite skeleton by an acidtreatment.

When an ion in zeolite is exchanged with a monovalent ion having a largeionic radius by ion exchange, the effective pore diameter becomes small,and on the other hand, when ion exchange is performed with a monovalention having a small ion radius, the effective pore diameter is close tothe pore diameter of the zeolite structure.

The effective pore diameter of zeolite can be reduced also by asilylation treatment. For example, by silylating a terminal silanol onthe outer surface of a zeolite membrane and further layering a silylatedlayer, the effective pore diameter of a pore facing the outer surface ofzeolite is reduced.

The separation function of the zeolite membrane composite used in thepresent invention is not particularly limited, and is exhibited bycontrolling the affinity and adsorption performance of gas molecules tothe zeolite membrane by controlling the surface physical properties ofthe zeolite. In other words, by controlling the polarity of zeolite, theadsorption performance of ammonia to the zeolite can be controlled tofacilitate permeation.

For example, as in the second embodiment of the present invention, bycontrolling the polarity of zeolite by the presence of nitrogen atoms,the affinity of ammonia for zeolite can be controlled to facilitatepermeation.

The polarity can be increased by substituting a Si atom of the zeoliteskeleton with an Al atom, whereby gas molecules having a high polaritysuch as ammonia can be actively adsorbed and permeated into the zeolitepores. It is also possible to control the polarity of resulting zeoliteby adding an atomic source other than an Al atomic source such as Ga,Fe, B, Ti, Zr, Sn, or Zn to an aqueous reaction mixture of hydrothermalsynthesis.

In addition, the permeation amount can be controlled by controlling notonly the pore diameter of zeolite but also the adsorption performance ofmolecules by ion exchange.

(Zeolite Membrane)

The zeolite membrane in the present invention is a membrane-likematerial composed of zeolite, and is preferably formed by crystallizingzeolite on the surface of a porous support. As a component constitutingthe membrane, an inorganic binder such as silica or alumina, an organicsubstance such as a polymer, a silylating agent for modifying thezeolite surface, or the like may be included as necessary in addition tozeolite.

A preferred zeolite contained in the zeolite membrane used in thepresent invention is as described above, and the zeolite contained inthe zeolite membrane may be one kind or a plurality of kinds thereof.Zeolite that is easily generated in a mixed phase such as ANA, GIS, orMER, or an amorphous component other than crystals may be contained.

One of the other embodiments of the present invention (zeolite membraneB) is a zeolite membrane containing zeolite, wherein the molar ratio ofnitrogen element to Al element determined by X-ray photoelectronspectroscopy is from 0.01 to 4. The zeolite membrane B is particularlypreferably used in the ammonia separation method of the firstembodiment.

The zeolite membrane B is preferably a zeolite membrane having a surfacein which the molar ratio of nitrogen atoms to Al atoms determined byX-ray photoelectron spectroscopy (XPS) is in a specific range. Here, thesurface of the zeolite membrane herein means a surface of the zeolitemembrane on the side of supplying a mixed gas composed of a plurality ofcomponents including ammonia and hydrogen and/or nitrogen for separatingammonia, and means a surface with which a porous support is not incontact when the zeolite membrane composite is used in the form of afilm formed on the porous support. Herein, the molar ratio of nitrogenatoms to Al atoms contained in the zeolite membrane is a numerical valuedetermined by X-ray photoelectron spectroscopy (XPS) under the followingmeasurement conditions.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

In the second embodiment of the present invention, the content ofnitrogen atoms contained in the zeolite membrane surface determined bythe XPS measurement is, in terms of molar ratio with respect to Al atomson the zeolite membrane surface, usually 0.01 or more, and preferably0.05 or more, more preferably 0.10 or more, still more preferably 0.20or more, especially preferably 0.30 or more, and particularly preferably0.50 or more, and the upper limit is not particularly limited since thelimit depends on the structure of a cationic species including anitrogen atom in zeolite contained in the zeolite membrane and theamount of nitrate ion remaining when a nitrate treatment of the zeolitemembrane is performed if necessary, and the limit is usually 4 or less,preferably 3 or less, and more preferably 1 or less. By using zeolitehaving such a specific nitrogen atom/Al atom ratio surface composition,the denseness and durability such as chemical reaction resistance orheat resistance of the zeolite membrane can be improved, and ammonia canbe separated from a mixed gas composed of a plurality of componentsincluding ammonia and hydrogen and/or nitrogen with high permeabilityand high selectivity. Here, the upper limit and lower limit values arevalid within the range of significant figures. Specifically, the upperlimit of 4 or less means less than 4.5, while 0.01 or more means 0.005or more.

In the second embodiment of the present invention, the nitrogen atomcontained in the zeolite membrane is a nitrogen atom derived from anammonium ion (NH₄ ⁺) or a cationic species obtained by protonating anorganic amine having from 1 to 20 carbon atoms such as methylamine,dimethylamine, trimethylamine, ethylamine, diethylamine, triethylamine,ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine,diethylenetriamine, triethylenetetraamine, aniline, methylaniline,benzylamine, methylbenzylamine, hexamethylenediamine,N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine,or piperidine contained in the zeolite described later, a nitrogen atomderived from an organic template (structure-directing agent) containinga nitrogen atom, when used when manufacturing zeolite membranes, anitrogen atom derived from a nitrate ion remaining during a nitratetreatment of the zeolite membrane performed if necessary, or the like.

The present embodiment is not yet known in detail and is notparticularly limited, and is characterized in that the effective porediameter of zeolite used for membrane separation is controlled by usingadsorption of ammonia on zeolite, and that ammonia is separated based onthe hopping mechanism of ammonia in zeolite pores as described below. Inthe present invention in which ammonia is separated by mainly utilizingthe hopping mechanism in pores accompanying adsorption/desorption ofammonia to zeolite as described above, the first important design factoris how to increase the adsorption affinity between ammonia in a supplygas mixture containing ammonia and the surface of the zeolite membraneover other gases such as hydrogen and nitrogen contained in the gasmixture. From this point of view, when a nitrogen atom in a form asdescribed above is present on the surface of the zeolite membrane, theadsorption affinity of ammonia to the zeolite membrane is increased byan interaction such as hydrogen bonding with ammonia in a supply gas,and as a result, the ammonia separation performance tends to beimproved.

One of the other embodiments of the present invention (zeolite membraneC) is a zeolite membrane containing zeolite, wherein the molar ratio ofSi element to Al element determined by X-ray photoelectron spectroscopyis from 2.0 to 10. The zeolite membrane C is preferably used in theammonia separation method of the first embodiment.

The zeolite membrane C used in the present invention is a zeolitemembrane having a surface in which the molar ratio of Si atoms to Alatoms determined by X-ray photoelectron spectroscopy (XPS) is in aspecific range. Herein, the molar ratio of Si atoms to Al atomscontained in the zeolite membrane is a numerical value determined byX-ray photoelectron spectroscopy (XPS) under the following measurementconditions.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

In the present embodiment, the content of Si atoms contained in thezeolite membrane surface determined by the XPS measurement is, in termsof molar ratio with respect to Al atoms on the zeolite membrane surface,2.0 or more, and preferably 2.5 or more, and more preferably 3.0 ormore, and the upper limit thereof is usually 10 or less, preferably 8.0or less, more preferably 7.0 or less, and particularly preferably 6.7 orless. In the present invention, as described below, the molar ratio ofSi atoms to Al atoms in the zeolite membrane can be controlled by amethod of controlling the SiO₂/Al₂O₃ ratio of zeolite in the zeolitemembrane, a method of treating the zeolite membrane with an aluminumsalt, or the like. As is apparent from the Example, by using a zeolitemembrane having such a specific Si atom/Al atom molar ratio, whenammonia is separated from a mixed gas composed of a plurality ofcomponents including ammonia and hydrogen and/or nitrogen, the densenessand durability such as chemical reaction resistance and heat resistanceof the zeolite membrane can be improved, high permeation selectivity andhigh permeability can be exhibited, and the separation heat stability athigh temperatures can be improved.

In the present embodiment, when controlling the content of Si atoms onthe surface of the zeolite membrane and, if necessary, controlling thecontent of nitrogen atoms contained in the zeolite membrane surfacedetermined by XPS measurement to a specific region, there is a tendencyfor the separation selectivity when separating ammonia from a mixed gascomposed of a plurality of components contained on the zeolite membranesurface to be remarkably improved, and therefore, it is preferable toallow nitrogen atoms to coexist on the zeolite membrane surface and tocontrol the content thereof appropriately. The content of nitrogen atomsthat, if necessary, coexist as described above on the surface of thezeolite membrane is, in terms of molar ratio with respect to Al atoms onthe zeolite membrane surface, usually 0.01 or more, and preferably 0.05or more, more preferably 0.10 or more, still more preferably 0.20 ormore, especially preferably 0.30 or more, and particularly preferably0.50 or more, and the upper limit is not particularly limited since thelimit depends on the structure of a cationic species including anitrogen atom in zeolite contained in the zeolite membrane and theamount of nitrate ion remaining when a nitrate treatment of the zeolitemembrane is performed if necessary, and the limit is usually 4 or less,preferably 3 or less, and more preferably 1 or less. By using zeolitehaving such a specific nitrogen atom/Al atom ratio surface composition,the denseness and durability such as chemical reaction resistance orheat resistance of the zeolite membrane can be improved, and ammonia canbe separated from a mixed gas composed of a plurality of componentsincluding ammonia and hydrogen and/or nitrogen with high selectivity,which is preferable. The above-described upper limit and lower limitvalues are valid within the range of significant figures. Specifically,the upper limit of 4 or less means less than 4.5, while 0.01 or moremeans 0.005 or more.

In the present embodiment, the nitrogen atom, when contained in thezeolite membrane, is a nitrogen atom derived from an ammonium ion (NH₄⁺) or a cationic species obtained by protonating an organic amine havingfrom 1 to 20 carbon atoms such as methylamine, dimethylamine,trimethylamine, ethylamine, diethylamine, triethylamine,ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine,diethylenetriamine, triethylenetetraamine, aniline, methylaniline,benzylamine, methylbenzylamine, hexamethylenediamine,N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine,or piperidine contained in the zeolite described later, a nitrogen atomderived from an organic template (structure-directing agent) containinga nitrogen atom used when manufacturing zeolite membranes, a nitrogenatom derived from a nitrate ion remaining during a nitrate treatment ofthe zeolite membrane performed if necessary, or the like.

In this embodiment, when the content of alkali metal atoms contained inthe zeolite membrane surface determined by XPS measurement is furthercontrolled within a specific range, the ammonia permeability whenseparating ammonia from a mixed gas composed of a plurality ofcomponents including ammonia and hydrogen and/or nitrogen tends to beimproved. Therefore, it is one of preferable embodiments to control thecontents thereof as necessary. As described above, examples of alkalimetal atoms that are present on the zeolite membrane surface ifnecessary include Li, Na, K, Rb, Cs, and two or more kinds thereof, andamong these, Li, Na, and Cs are preferable, and Na is more preferablebecause Na is excellent in ammonia separation performance and is ageneral-purpose alkali metal. These alkali metal atoms exist in the formof a cation as an ion pair of an Al site in zeolite constituting thezeolite membrane, and are usually introduced into the zeolite by an ionexchange treatment of synthesized zeolite membrane as described below.The content of alkali metal atoms to be present on the zeolite membranesurface as necessary, in molar ratio with respect to Al atoms on thezeolite membrane surface, is 0.01 or more, and preferably 0.02 or more,more preferably 0.03 or more, still more preferably 0.04 or more, andparticularly preferably 0.05 or more, and the upper limit is usually0.10 molar equivalent or less, and preferably 0.070 molar equivalent orless, more preferably 0.065 molar equivalent or less, more preferably0.060 molar equivalent or less, and particularly preferably 055 molarequivalent or less. Controlling the content of alkali metal atoms withinthe above range is preferable because the ammonia permeability tends tobe improved while the ammonia separation selectivity is increased. Themolar ratio of alkali metal atoms to Al atoms in the zeolite membranecan be controlled by adjusting the ion exchange amount during the ionexchange treatment of zeolite, as will be described below.

The present embodiment is not yet known in detail and is notparticularly limited, and is characterized in that the effective porediameter of zeolite used for membrane separation is controlled by usingadsorption of ammonia on zeolite, and that ammonia is separated based onthe hopping mechanism of ammonia in zeolite pores as described below. Inthe present invention in which ammonia is separated by mainly utilizingthe hopping mechanism in pores accompanying adsorption/desorption ofammonia to zeolite as described above, the first important design factoris how to increase the adsorption affinity between ammonia in a supplygas mixture containing ammonia and the surface of the zeolite membraneover other gases such as hydrogen and nitrogen contained in the gasmixture. From this point of view, when more Al atoms are present on thesurface of the zeolite membrane, the polarity of the surface of thezeolite membrane is changed and the adsorption affinity with ammonia ina supply gas is increased, and therefore, the ammonia separationperformance is improved. In the present embodiment, the content of Alatoms on the surface of the zeolite membrane is controlled by theSiO₂/Al₂O₃ ratio of zeolite constituting the zeolite membrane, analuminum salt treatment after formation of the zeolite membrane, or thelike. In particular, since the latter aluminum salt treatment also hasan effect of sealing fine defects present on the zeolite membranesurface, the treatment can improve the denseness of the zeolite membraneand durability such as chemical reaction resistance and heat resistance,and greatly contributes to the improvement of the separation heatstability at high temperatures of the zeolite membrane, which is one ofthe problems of the present invention.

Another embodiment of the present invention (zeolite membrane D) is azeolite membrane containing zeolite and having a molar ratio of alkalimetal element to Al element determined by X-ray photoelectronspectroscopy of from 0.01 to 0.070. The zeolite membrane D isparticularly preferably used in the ammonia separation method of thefirst embodiment.

The zeolite membrane D used in the fourth embodiment of the presentinvention is preferably a zeolite membrane including a surface in whichthe molar ratio of alkali metal atoms to Al atoms determined by X-rayphotoelectron spectroscopy (XPS) is in a specific range. Herein, themolar ratio of alkali metal atoms to Al atoms contained in the zeolitemembrane is a numerical value determined by X-ray photoelectronspectroscopy (XPS) under the following measurement conditions.

(Measurement Conditions)

X-ray source for measurement: Monochromatic Al-Kα ray, output 16 kV-34 W

Background determination method for quantitative calculation: Shirleymethod

In the present embodiment, examples of alkali metal atoms contained inthe zeolite membrane surface determined by the XPS measurement includeLi, Na, K, Rb, Cs, and two or more kinds thereof, and among these, Li,Na, and Cs are preferable, and Na is more preferable because Na isexcellent in ammonia separation performance and is a general-purposealkali metal. These alkali metal atoms exist in the form of a cation asan ion pair of an Al site in zeolite constituting the zeolite membrane,and are usually introduced into the zeolite by an ion exchange treatmentof synthesized zeolite membrane as described below.

In this embodiment, it is important to control the content of alkalimetal atoms contained in the zeolite membrane surface determined by theXPS measurement, and the content, in molar ratio with respect to Alatoms on the zeolite membrane surface, is 0.01 or more, and preferably0.02 or more, more preferably 0.03 or more, still more preferably 0.04or more, and particularly preferably 0.05 or more, and the upper limitis usually 0.10 molar equivalent or less, and preferably 0.070 molarequivalent or less, more preferably 0.065 molar equivalent or less, morepreferably 0.060 molar equivalent or less, and particularly preferably055 molar equivalent or less. By controlling the content of the alkalimetal element within the above range, the ammonia permeability can beimproved while improving the ammonia separation selectivity, as isapparent from the Example and Reference Example.

In the present embodiment, the molar ratio of alkali metal atoms to Alatoms in the zeolite membrane can be controlled by adjusting the ionexchange amount during the ion exchange treatment of zeolite, as will bedescribed below. By using a zeolite membrane having such a specificalkali metal atom/Al atom molar ratio, when ammonia is separated from amixed gas composed of a plurality of components including ammonia andhydrogen and/or nitrogen, while exhibiting high permeation selectivity,the ammonia permeability can be improved as compared with the zeolitemembrane not containing the alkali metal atom.

In the present embodiment, when controlling the content of alkali metalatoms on the surface of the zeolite membrane and, if necessary,controlling the content of nitrogen atoms contained in the zeolitemembrane surface determined by XPS measurement to a specific region,there is a tendency for the separation selectivity when separatingammonia from a mixed gas composed of a plurality of components includingammonia and hydrogen and/or nitrogen to be remarkably improved, andtherefore, it is preferable to allow alkali metal atoms and nitrogenatoms to coexist on the zeolite membrane surface and to control thecontent thereof appropriately. The content of nitrogen atoms, whencoexist as described above on the surface of the zeolite membrane, is,in terms of molar ratio with respect to Al atoms on the zeolite membranesurface, usually 0.01 or more, and preferably 0.05 or more, morepreferably 0.10 or more, still more preferably 0.20 or more, especiallypreferably 0.30 or more, and particularly preferably 0.50 or more, andthe upper limit is not particularly limited since the limit depends onthe structure of a cationic species including a nitrogen atom in zeolitecontained in the zeolite membrane and the amount of nitrate ionremaining when a nitrate treatment of the zeolite membrane is performedif necessary, and the limit is usually 4 or less, preferably 3 or less,and more preferably 1 or less. By using zeolite having such a specificnitrogen atom/Al atom ratio surface composition, the denseness anddurability such as chemical reaction resistance or heat resistance ofthe zeolite membrane can be improved, and ammonia can be separated froma mixed gas composed of a plurality of components including ammonia andhydrogen and/or nitrogen with high selectivity, which is preferable. Theabove-described upper limit and lower limit values are valid within therange of significant figures. Specifically, the upper limit of 4 or lessmeans less than 4.5, while 0.01 or more means 0.005 or more.

In the present invention, the nitrogen atom, when contained in thezeolite membrane, is a nitrogen atom derived from an ammonium ion (NH₄⁺) or a cationic species obtained by protonating an organic amine havingfrom 1 to 20 carbon atoms such as methylamine, dimethylamine,trimethylamine, ethylamine, diethylamine, triethylamine,ethylenediamine, dimethylethylenediamine, tetramethylethylenediamine,diethylenetriamine, triethylenetetraamine, aniline, methylaniline,benzylamine, methylbenzylamine, hexamethylenediamine,N,N-diisopropylethylamine, N,N,N-trimethyl-1-adamantanamine, pyridine,or piperidine contained in the zeolite described later, a nitrogen atomderived from an organic template (structure-directing agent) containinga nitrogen atom used when manufacturing zeolite membranes, a nitrogenatom derived from a nitrate ion remaining during a nitrate treatment ofthe zeolite membrane performed if necessary, or the like.

The present embodiment is not yet known in detail and is notparticularly limited, and is characterized in that the effective porediameter of zeolite used for membrane separation is controlled by usingadsorption of ammonia on zeolite, and that ammonia is separated based onthe hopping mechanism of ammonia in zeolite pores as described below. Inthe present invention in which ammonia is separated by mainly utilizingthe hopping mechanism in pores accompanying adsorption/desorption ofammonia to zeolite as described above, while the ammonia separationselectivity from a mixed gas composed of a plurality of componentsincluding ammonia and hydrogen and/or nitrogen improves by a blockingeffect by adsorption of ammonia to an Al site in a zeolite pore, sincethe adsorption power of ammonia to the Al site is high, there exists atendency for permeation performance (permeability) to be impaired. Incontrast, by allowing the alkali metal atom of the present invention toexist in a specific amount in the form of a cation as an ion pair of theAl site in zeolite constituting the zeolite membrane, the amount ofammonia adsorbed on the Al site can be controlled, and on the otherhand, the ammonia separation selectivity can be maintained by the sizeof the alkali metal cation. By these mechanisms, the permeationperformance can be enhanced while maintaining the ammonia separationselectivity. Specifically, it is important to control the content ofalkali metal atoms to Al atoms in the zeolite in a molar ratio of from0.01 to 0.070, and it is considered that when the content is less than0.01, the ammonia permeability decreases due to adsorption of ammonia toan Al site, whereas when the content is higher than 0.20, a blockingeffect by adsorption of ammonia on an Al site is weakened and theammonia separation selectivity decreases.

Another aspect of the present invention (zeolite membrane composite E)is a zeolite membrane composite for ammonia separation including aporous support and a zeolite membrane containing zeolite on the surfacethereof, characterized in that the change rate of the thermal expansioncoefficient at 300° C. with respect to the thermal expansion coefficientat 30° C. of the zeolite and the thermal expansion coefficient at 400°C. are within a specific range. The zeolite membrane composite E ispreferably used in the ammonia separation method of the firstembodiment.

Specifically, the change rate of thermal expansion coefficient at 300°C. with respect to thermal expansion coefficient at 30° C. of thezeolite is equal to or within ±0.25% and the change rate of thermalexpansion coefficient at 400° C. with respect to thermal expansioncoefficient at 30° C. of the zeolite is equal to or within ±0.35%.

The thermal expansion coefficient that defines the zeolite of thepresent embodiment is a numerical value calculated under the followingconditions. Herein, when the numerical value of the thermal expansioncoefficient is positive, the value indicates that the zeolite hasexpanded, and when the value is negative, the value indicates that thezeolite has contracted.

(Measurement Method of Change Rate of Thermal Expansion Coefficient)

In the present invention, the change rate of thermal expansioncoefficient at a predetermined temperature with respect to the thermalexpansion coefficient of zeolite at 30° C. can be obtained by thefollowing formula (1) by obtaining a crystallite constant measured at30° C. and a predetermined temperature by a high temperature XRDmeasurement method under the following conditions.

(Specifications of High Temperature XRD Measurement Apparatus)

TABLE 1 Apparatus name New D8 ADVANCE manufactured by Bruker CorporationOptical system Bragg-Brentano optical system Optical Incident sideEnclosed X-ray tube (CuKα) system Seller Slit (2.5°) specificationsDivergence Slit (Variable Slit) Sample stage High-temperature samplestage HTK1200 Light-receiving side Semiconductor array detector (LynxEye) Ni-filter Seller Slit (2.5°) Goniometer radius 280 mm

(Measurement Conditions)

TABLE 2 X-ray output 40 kV (CuKα) 40 mA Scanning axis θ/2θ Scanningrange (2θ) 5.0-70.0° Measurement mode Continuous Read width 0.02°Counting time 19.2 sec (0.1 sec × 192 ch) Automatic variable slit * 6 mm(irradiation width)Measurement atmosphere: AirTemperature rise condition: 20° C./minMeasurement method: XRD measurement is carried out after holding at themeasurement temperature for 5 minutes.Measurement data is subjected to fixed slit correction using a variableslit.

Change rate of thermal expansion coefficient=(crystal lattice constantmeasured at predetermined temperature)+(crystal lattice constantmeasured at 30° C.)−1  (1)

The change rate of the thermal expansion coefficient at 300° C. withrespect to the thermal expansion coefficient at 30° C. of the zeolite ofthe present invention has an absolute value of 0.25% or less, preferably0.20% or less, more preferably 0.15% or less, particularly preferably0.10% or less, and most preferably 0.05% or less. In other words, thechange rate of thermal expansion coefficient at 300° C. with respect tothe thermal expansion coefficient at 30° C. of the zeolite is within±0.25%, preferably within ±0.20%, more preferably within ±0.15%,particularly preferably within ±0.10%, and most preferably within±0.05%.

On the other hand, the change rate of thermal expansion coefficient at400° C. with respect to the thermal expansion coefficient at 30° C. ofthe zeolite has an absolute value of 0.35% or less, preferably 0.30% orless, more preferably 0.25% or less, especially preferably 0.20% orless, particularly preferably 0.15% or less, and most preferably 0.10%or less. In other words, the change rate of thermal expansioncoefficient at 400° C. with respect to the thermal expansion coefficientat 30° C. of the zeolite is within ±0.35%, preferably within ±0.30%,more preferably within ±0.25%, especially preferably within ±0.20%,particularly preferably within ±0.15%, and most preferably within±0.10%. When ammonia in a gas mixture composed of a plurality ofcomponents including ammonia and hydrogen and/or nitrogen is allowed topermeate through a zeolite membrane composite in which a zeoliteexhibiting a low change rate of thermal expansion coefficient is formedinto a membrane on a porous support, and when the temperature of thecomposite is raised to a temperature higher than 200° C., especially atemperature higher than 250° C., or even a temperature higher than 300°C., a crack in a zeolite grain boundary due to the thermal expansion(shrinkage) of the zeolite hardly occur, and therefore, ammonia can beefficiently separated to the permeation side with high permeability evenunder high temperature conditions. In particular, as described for RHOzeolite of the Example, a zeolite membrane composite using zeoliteexhibiting such a thermal expansion coefficient exhibits stable and highseparation performance as a membrane under high temperature conditionseven if the membrane exhibits a nonlinear thermal expansion/contractionbehavior with respect to temperature. Here, the nonlinear thermalexpansion/contraction behavior with respect to temperature refers to abehavior that does not monotonously expand or contract with temperature,in other words, for example, a thermal expansion or contraction behavioris exhibited in a certain temperature range, but opposite behaviors orthermal contraction in the former case and thermal expansion behavior inthe latter case are observed in other temperature ranges.

The reason for this is not yet known in detail and is not particularlylimited to the following, but is considered that, even if zeolitethermally contracts or expands during a temperature rising process, thezeolite moves favorably on a support, forming a dense zeolite membranecomposite that exhibits high separation performance suitable forhigh-temperature conditions without generating a crack. Accordingly,when ammonia is stably separated under high temperature conditions,zeolite that exhibits nonlinear thermal expansion/contraction behaviorin a temperature rising process may be used. The zeolite used in thepresent invention is not particularly limited, and examples thereofinclude RHO (D. R. Corbin. etaL. J. Am. Chem. Soc, 112, 4821-4830), MFI,AFI, and DDR (Park S, H. etaL. Stud. Surf Sci. Catal. 1997, 105,1989-1994).

The absolute value of the change rate of the thermal expansioncoefficient at 400° C. with respect to the thermal expansion coefficientat 30° C. with respect to the change rate of the thermal expansioncoefficient at 300° C. with respect to the thermal expansion coefficientat 30° C. of the zeolite of the present embodiment as a ratio is usually120% or less, and preferably 115% or less, more preferably 110% or less,particularly preferably 105% or less, and most preferably 103% or less.For example, even when a heterogeneous exotherm occurs in a reactor atthe beginning of a reaction when ammonia production is started, since azeolite membrane composite in which zeolite exhibiting such change rateratio of specific thermal expansion coefficients between specifictemperatures is formed into a membrane on a porous support can suppressa crack at a grain boundary due to local thermal expansion (contraction)of the zeolite, ammonia can be stably separated to the permeation sideefficiently with high permeability.

When the zeolite membrane composite of this embodiment is preparedthrough a step of depositing zeolite having a change rate of thermalexpansion coefficient within a specific range as a seed crystal on aporous support when synthesizing a membrane, it is often preferable tostably separate ammonia with high selectivity even under hightemperature conditions. The absolute value of the change rate of thermalexpansion coefficient at 300° C. with respect to the thermal expansioncoefficient at 30° C. of zeolite used as a seed crystal for preparingsuch a zeolite membrane composite is 0.25% or less, and preferably 0.20%or less, more preferably 0.15% or less, particularly preferably 0.10% orless, and most preferably 0.05% or less. On the other hand, the absolutevalue of the change rate of thermal expansion coefficient at 400° C.with respect to the thermal expansion coefficient at 30° C. is usually0.30% or less, and preferably 0.25% or less, more preferably 0.20% orless, particularly preferably 0.15% or less, and most preferably 0.10%or less.

The change rate of thermal expansion coefficient at a specifictemperature of the zeolite, which is a characteristic of the presentembodiment, can be controlled by appropriately selecting a cationicspecies of zeolite to be used as will be described below. For example,regarding the relationship between a cationic species of RHO zeolite andthe thermal expansion coefficient, as described in Chemical,Communications, 2000, 2221-2222, it is known that the thermal expansioncoefficient varies depending on the cationic species contained inzeolite. Therefore, in order to obtain a zeolite membrane composite thatstably separates ammonia with high selectivity even under the hightemperature conditions of the present embodiment, it is particularlyimportant to select a specific cationic species among RHO zeolites. Onthe other hand, regarding the thermal expansion coefficient of the MFIzeolite described in Examples of the present embodiment, a zeolitemembrane composite exhibiting the characteristics of the presentembodiment can be produced by selecting an appropriate cationic speciesin the zeolite as in the case of the RHO zeolite.

The cationic species contained in the zeolite of the present embodimentis preferably a cationic species that easily coordinates to an ionexchange site of the zeolite, such as a cationic species selected fromthe group of elements of group 1, group 2, group 8, group 9, group 10,group 11, and group 12 of the periodic table, NH₄ ⁺, and two or morekinds of cationic species thereof, and more preferably a cationicspecies selected from group 1 and group 2 elements of the periodictable, NH₄ ⁺, and two or more kinds of cationic species thereof.

The zeolite used in the present embodiment is an aluminosilicate. TheSiO₂/Al₂O₃ molar ratio of aluminosilicate is not particularly limited,and is usually 6 or more, preferably 7 or more, more preferably 8 ormore, still more preferably 10 or more, especially preferably 11 ormore, particularly preferably 12 or more, and most preferably 13 ormore. The upper limit is usually an amount in which Al is contained inan impurity level, and the SiO₂/Al₂O₃ molar ratio is usually 500 orless, preferably 100 or less, more preferably 90 or less, still morepreferably 80 or less, especially preferably 70 or less, particularlypreferably 50 or less, and most preferably 30 or less. By using suchzeolite with an SiO₂/Al₂O₃ molar ratio in a specific region, thedenseness of a zeolite membrane and durability such as chemical reactionresistance and heat resistance can be improved. From the viewpoint ofthe separation performance of allowing ammonia to permeate from a gasmixture composed of a plurality of components including ammonia andhydrogen and/or nitrogen, as described above, from a reason that theacid point of Al element becomes an adsorption site of ammonia, it ispreferable to use a zeolite containing a specific amount of A1, and byusing zeolite having the above-described SiO₂/Al₂O₃ molar ratio, ammoniacan be separated with high permeability and high selectivity. TheSiO₂/Al₂O₃ molar ratio of zeolite can be adjusted by the reactionconditions of hydrothermal synthesis described below.

The thickness of the zeolite membrane used in the present invention isnot particularly limited, and is usually 0.1 μm or more, preferably 0.3μm or more, more preferably 0.5 μm or more, still more preferably 0.7 μmor more, still more preferably 1.0 μm or more, and particularlypreferably 1.5 μm or more. The thickness is usually 100 μm or less,preferably 60 μm or less, more preferably 20 μm or less, still morepreferably 15 μm or less, still more preferably 10 μm or less, andparticularly preferably 5 μm or less. When the thickness of a zeolitemembrane is not less than the above-described lower limit, a defect isless likely to occur and the separation performance tends to befavorable. When the thickness of a zeolite membrane is not more than theabove-described upper limit value, the permeation performance tends toimprove, and in addition, in a high temperature region, a crack is lesslikely to occur in the zeolite membrane due to an increase intemperature, and thus there is a tendency that a decrease in permeationselectivity at a high temperature can be suppressed.

The average primary particle diameter of zeolite forming a zeolitemembrane is not particularly limited, and is usually 30 nm or more,preferably 50 nm or more, and more preferably 100 nm or more, and theupper limit is less than or equal to the thickness of the membrane. Whenthe average primary particle size of zeolite is not less than theabove-described lower limit value, the grain boundary of the zeolite canbe reduced, and therefore, favorable permeation selectivity can beobtained. Therefore, it is most preferable that the average primaryparticle diameter of the zeolite is the same as the thickness of thezeolite membrane. In this case, the grain boundary of zeolite can beminimized. A zeolite membrane obtained by hydrothermal synthesisdescribed below is preferable because the particle size of zeolite andthe thickness of the membrane is the same in some cases.

In the present invention, the average primary particle size is obtainedas an average value by measuring the primary particle size of 30 or morearbitrarily selected particles in observation of the surface or fracturesurface of the zeolite membrane composite of the present invention witha scanning electron microscope.

The shape of a zeolite membrane is not particularly limited, and anyshape such as a tubular shape, a hollow fiber shape, a monolith type,and a honeycomb type can be adopted. The size of a zeolite membrane isnot particularly limited, and for example, the zeolite membrane isformed as a zeolite membrane composite formed on a porous support havinga size described below.

(Porous Support)

In the present invention, a zeolite membrane is preferably formed on thesurface of a porous support. Preferably, zeolite is crystallized in theform of a film on the porous support.

A porous support used in the present invention preferably has chemicalstability such that zeolite can be crystallized into a membrane on thesurface. Examples of a suitable porous support include a gas-permeableporous polymer such as polysulfone, cellulose acetate, aromaticpolyamide, vinylidene fluoride, polyethersulfone, polyacrylonitrile,polyethylene, polypropylene, polytetrafluoroethylene, or polyimide; aceramic sintered body such as silica, α-alumina, γ-alumina, mullite,zirconia, titania, yttria, silicon nitride, or silicon carbide; asintered body or mesh-like molding of a metal such as iron, bronze, orstainless; and an inorganic porous material such as a glass or carbonmolding. From the reason that the mechanical strength, deformationresistance, heat stability, and reaction resistance at high temperaturesof the support are excellent, as a porous support for separating ammoniain a high temperature region, among these, an inorganic porous supportsuch as a ceramic sintered body, a metal sintered body, a glass orcarbon molding is preferable. An inorganic porous support is preferablyobtained by sintering ceramics, which is a solid material whose basiccomponent or most of the inorganic support is composed of an inorganicnonmetallic substance.

Examples of preferable ceramic sintered bodies include ceramic sinteredbodies including α-alumina, γ-alumina, silica, mullite, zirconia,titania, yttria, silicon nitride, and silicon carbide as describedabove, but these may be single sintered bodies or may be a mixture of aplurality of sintered bodies. Since these ceramic sintered bodies may bepartly zeoliticized during synthesis of a zeolite membrane, thisincreases adhesion between a porous support and the zeolite membrane, sothat the durability of the zeolite membrane composite can be improved.

In particular, an inorganic porous support containing at least one ofalumina, silica, and mullite is more preferable since binding of theinorganic porous support and zeolite becomes strong and a dense zeolitemembrane with high separation performance is easily formed due to easeof partial zeolitization of the inorganic porous support.

The porous support used in the present invention preferably has anaction of crystallizing zeolite formed on the porous support on thesurface thereof (hereinafter, also referred to as “porous supportsurface”).

The pore diameter on the porous support surface is preferablycontrolled. The average pore diameter of a porous support near theporous support surface is usually 0.02 μm or more, and preferably 0.05μm or more, more preferably 0.1 μm or more, still more preferably 0.15μm or more, further preferably 0.5 μm or more, particularly preferably0.7 μm or more, and most preferably 1.0 μm or more, and is usually 20 μmor less, and preferably 10 μm or less, more preferably 5 μm or less, andparticularly preferably 2 μm or less. By using a porous support having apore diameter in such a range, a dense zeolite membrane that improvesthe ammonia permeation selectivity can be formed.

The surface of a porous support is preferably smooth, and the surfacemay be polished with a file or the like as necessary.

The pore diameter of a portion of the porous support used in the presentinvention other than the vicinity of the porous support surface is notlimited and does not need to be controlled in particular, and theporosity thereof is usually 20% or more, and more preferably 30% ormore, and usually 60% or less, and preferably 50% or less. The porosityof the portion other than the vicinity of the porous support surfaceaffects the permeation flow rate when separating gas and liquid. Whenthe porosity is not less than the above-described lower limit, apermeated substance tends to diffuse, and when the porosity is not morethan the above-described upper limit, the strength of the porous supporttends to be prevented from decreasing. As a method for controlling thepermeation flow rate, a porous support in which porous bodies havingdifferent porosities are combined in layers may be used.

The shape of a porous support used in the present invention is notlimited as long as the shape can effectively separate a mixed gas orliquid mixture, and specific examples thereof include flat, tubular,cylindrical, honeycomb with many through holes or monolith. The size andthe like of the porous support are any, and may be appropriatelyselected and adjusted in such a manner that a desired zeolite membranecomposite is obtained. Among these, the shape of a porous support may bepreferably tubular.

The length of a tubular porous support is not particularly limited, andis usually 2 cm or more, and preferably 4 cm or more, more preferably 5cm or more, particularly preferably 10 cm or more, especially preferably40 cm or more, and most preferably 50 cm or more, and is usually 200 cmor less, and preferably 150 cm or less, and more preferably 100 cm orless. When the length of a porous support is equal to or more than theabove-described lower limit value, the amount of separation treatment ofa mixed gas per one porous support can be increased, and therefore, theequipment cost can be reduced. When the length is less than or equal tothe above-described upper limit, production of a zeolite membranecomposite can be simplified, and further, a problem such as easybreakage due to vibration during use can be prevented.

The inner diameter of a tubular porous support is usually 0.1 cm ormore, and preferably 0.2 cm or more, more preferably 0.3 cm or more, andparticularly preferably 0.4 cm or more, and is usually 2 cm or less, andpreferably 1.5 cm or less, more preferably 1.2 cm or less, andparticularly preferably 1.0 cm or less. The outer diameter is usually0.2 cm or more, and preferably 0.3 cm or more, more preferably 0.6 cm ormore, and particularly preferably 1.0 cm or more, and usually 2.5 cm orless, and preferably 1.7 cm or less, and more preferably 1.3 cm or less.The wall thickness of a tubular porous support is usually 0.1 mm ormore, and preferably 0.3 mm or more, more preferably 0.5 mm or more,still more preferably 0.7 mm or more, still more preferably 1.0 mm ormore, and particularly preferably 1.2 mm or more, and is usually 4 mm orless, and preferably 3 mm or less, and more preferably 2 mm or less.When the inner diameter, the outer diameter, and the wall thickness of atubular porous support are equal to or higher than the above-describedlower limit values, respectively, the strength of the support can beimproved and the support can be difficult to break. When the innerdiameter and the outer diameter of a tubular support are equal to orless than the above-described upper limit values, respectively, the sizeof equipment associated with separation of ammonia can be reduced, whichcan be economically advantageous. When the thickness of a tubularsupport is not more than the above-described upper limit value, thepermeation performance tends to be improved.

The absolute value of the change rate of thermal expansion coefficientat 300° C. with respect to the thermal expansion coefficient at 30° C.of the porous support used in the fifth embodiment is 0.25% or less, andpreferably 0.20% or less, more preferably 0.15% or less, particularlypreferably 0.10% or less, and most preferably 0.05% or less. In otherwords, the change rate of thermal expansion coefficient at 300° C. withrespect to the thermal expansion coefficient at 30° C. of the poroussupport of the zeolite membrane composite E is within ±0.25%, andpreferably within ±0.20%, more preferably within ±0.15%, particularlypreferably within ±0.10%, and most preferably within ±0.05%. On theother hand, the absolute value of the change rate of thermal expansioncoefficient at 400° C. with respect to the thermal expansion coefficientat 30° C. of the porous support of the zeolite membrane composite E isusually 0.30% or less, and preferably 0.25% or less, more preferably0.20% or less, particularly preferably 0.15% or less, and mostpreferably 0.10% or less. In other words, the change rate of thermalexpansion coefficient at 400° C. with respect to the thermal expansioncoefficient at 30° C. of the porous support is within ±0.30%, andpreferably within ±0.25%, more preferably within ±0.20%, particularlypreferably within ±0.15%, and most preferably within ±0.10%. When azeolite membrane composite formed on a porous support exhibiting such alow thermal expansion coefficient is heated for the purpose ofpermeating ammonia of a gas mixture composed of a plurality ofcomponents including ammonia and hydrogen and/or nitrogen even under,for example, temperature conditions exceeding 200° C., or 300° C., azeolite membrane is less likely to crack following thermal expansion(contraction) of the porous support, and therefore can efficientlyseparate ammonia to the permeation side with high permeability andstability even under high temperature conditions.

The absolute value of the ratio of the change rate of thermal expansioncoefficient at 400° C. with respect to the thermal expansion coefficientat 30° C. with respect to the change rate of thermal expansioncoefficient at 300° C. with respect to the thermal expansion coefficientat 30° C. of the porous support used in the fifth embodiment is usually120% or less, and preferably 115% or less, more preferably 110% or less,especially preferably 105% or less, and most preferably 103% or less.For example, since occurrence of a crack in the zeolite membranefollowing the local thermal expansion (contraction) of the poroussupport can be suppressed even when inhomogeneous heat generation occursin a reactor during ammonia production, a zeolite membrane compositeformed on a porous support exhibiting a specific thermal expansioncoefficient ratio between such specific temperatures can efficientlyseparate ammonia to the permeation side with high permeability stablyeven under high temperature conditions.

(Zeolite Membrane Composite)

In the present invention, a zeolite membrane is preferably used as azeolite membrane composite including at least zeolite and a support.

In the present invention, the zeolite membrane composite is one in whichthe above-described zeolite is membrane-like, and preferablycrystallized and fixed on the surface or the like of the above-describedporous support, and is, in some cases, preferably one in which a part ofthe zeolite is fixed to the inside of the support.

As the zeolite membrane composite, for example, one obtained bycrystallizing zeolite into a membrane by hydrothermal synthesis on thesurface of a porous support or the like is preferable.

The position of a zeolite membrane on a porous support is notparticularly limited, and when a tubular support is used, the zeolitemembrane may be formed on the outer surface, may be formed on the innersurface, or may be formed on both sides depending on a system to beapplied. A zeolite membrane may be formed by being layered on thesurface of a support, or may be crystallized in such a manner to fillpores of a surface layer of the support. In this case, it is importantthat there are no cracks or continuous micropores inside a crystallizedmembrane layer, and it is preferable to form a so-called dense membranefrom the viewpoint of improving separability.

The zeolite and the support constituting the zeolite membrane compositeare not particularly limited, and preferably used in any combination ofthe above-described zeolites and supports. Among these, specificexamples of a particularly preferable combination of zeolite and poroussupport include MFI zeolite-porous alumina support, RHO zeolite-porousalumina support, DDR zeolite-porous alumina support, AFI zeolite-porousalumina support, CHA zeolite-porous alumina support, and AEIzeolite-porous alumina support. CHA zeolite-porous alumina support, MFIzeolite-porous alumina support, or RHO zeolite-porous alumina support ispreferable, and MFI zeolite-porous alumina support or RHO zeolite-porousalumina support is more preferable.

In one embodiment of the present invention (zeolite membranes B to E),MFI zeolite-porous alumina support, or RHO zeolite-porous aluminasupport is preferable, and RHO zeolite-porous alumina support is morepreferable.

<Method for Producing Zeolite Membrane Composite>

In the present invention, the method for forming a zeolite membranecomposite is not particularly limited as long as the above-describedzeolite membrane can be formed on a porous support, and the zeolitemembrane composite can be produced by a known method. Any method such as(1) a method of crystallizing zeolite on a support in a membrane form,(2) a method of fixing zeolite to a support with an inorganic binder oran organic binder, (3) a method of fixing a polymer in which zeolite isdispersed to a support, or (4) a method of fixing zeolite to a supportby impregnating the support with a slurry of zeolite and optionallysucking the support can be used.

Among these, a method of crystallizing zeolite on a porous support intoa membrane form is particularly preferable. The crystallization methodis not particularly limited, and a method of crystallizing zeolite onthe surface of a support by putting the support in a reaction mixturefor hydrothermal synthesis used for zeolite production (hereinafter,sometimes referred to as “aqueous reaction mixture”) and directlyhydrothermally synthesizing is preferable.

In this case, a zeolite membrane composite can be produced, for example,by placing an aqueous reaction mixture that is homogenized by adjustingthe composition in a heat and pressure vessel such as an autoclave witha porous support therein and sealing and heating for a certain time.

The aqueous reaction mixture contains a Si atom source, an Al atomsource, an alkali source, and water, and further contains an organictemplate (structure-directing agent) if necessary.

In order to better understand a method for producing a zeolite membranecomposite, a method for producing an RHO zeolite membrane composite anda method for producing an MFI zeolite membrane composite asrepresentative examples will be described in detail hereinafter, but thezeolite membrane and the production method of the present invention arenot limited thereto.

(RHO Zeolite Membrane)

RHO zeolite used in the present invention indicates zeolite having astructure represented by RHO which is a code defined by theInternational Zeolite Association (IZA). RHO zeolite has a structurecharacterized by having three-dimensional pores composed of 8-memberedoxygen rings having a diameter of 3.6×3.6 Å, and the structure ischaracterized by X-ray diffraction data.

The framework density of the RHO zeolite used in the present inventionis 14.1 T/1,000 Å. The framework density means the number of atomsconstituting a skeleton of zeolite other than oxygen per 1,000 Å³, andthis value is determined by the structure of the zeolite. Therelationship between the framework density and the structure of zeoliteis shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007ELSEVIER.

(MFI Zeolite Membrane)

MFI zeolite used in the present invention indicates zeolite having astructure represented by MFI which is a code defined by theInternational Zeolite Association (IZA). MFI zeolite has a structurecharacterized by having three-dimensional pores composed of 10-memberedoxygen rings having a diameter of 5.1×5.5 Å or 5.3×5.6 Å, and thestructure is characterized by X-ray diffraction data.

The framework density of the MFI zeolite used in the present inventionis 17.9 T/1,000 Å. The framework density means the number of atomsconstituting a skeleton of zeolite other than oxygen per 1,000 Å³, andthis value is determined by the structure of the zeolite. Therelationship between the framework density and the structure of zeoliteis shown in ATLAS OF ZEOLITE FRAMEWORK TYPES Fifth Revised Edition 2007ELSEVIER.

<Method for Producing RHO Zeolite Membrane> (Silicon Atom Source)

A silicon (Si) atom source used in an aqueous reaction mixture is notparticularly limited, and examples thereof include aluminosilicatezeolite, fumed silica, colloidal silica, amorphous silica, a siliconalkoxide such as sodium silicate, methyl silicate, ethyl silicate, ortrimethylethoxysilane, tetraethyl orthosilicate, and aluminosilicategel, and preferred examples thereof include aluminosilicate zeolite,fumed silica, colloidal silica, amorphous silica, sodium silicate,methyl silicate, ethyl silicate, silicon alkoxide, and aluminosilicategel. These may be used singly or in combination of two or more kindsthereof.

A Si atom source is used in such a manner that the amount of other rawmaterials used with respect to the Si atom source is within the above-or below-described preferred range.

(Aluminum Atom Source)

An aluminum (Al) atom source used for producing a porous support-RHOzeolite membrane composite is not particularly limited, and examplesthereof include aluminosilicate zeolite, amorphous aluminum hydroxide,aluminum hydroxide with gibbsite structure, aluminum hydroxide withbayerite structure, aluminum nitrate, aluminum sulfate, aluminum oxide,sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, andaluminosilicate gel. Aluminosilicate zeolite, amorphous aluminumhydroxide, sodium aluminate, boehmite, pseudoboehmite, aluminumalkoxide, and aluminosilicate gel are preferable, and aluminosilicatezeolite, amorphous aluminum hydroxide, sodium aluminate, andaluminosilicate gel are particularly preferable. These may be usedsingly or in combination of two or more kinds thereof.

An aluminosilicate zeolite may be used singly or in combination of twoor more kinds thereof. When an aluminosilicate zeolite is used as an Alatom source, the above-described aluminosilicate zeolite is preferably50% by weight or more, particularly from 70 to 100% by weight, andespecially from 90 to 100% by weight of the total Al atom source. Whenan aluminosilicate zeolite is used as a Si atom source, thealuminosilicate zeolite is preferably 50% by mass or more, particularlyfrom 70 to 100% by mass, and particularly from 90 to 100% by mass of thetotal Si atom source. When the ratio of an aluminosilicate zeolite iswithin this range, an RHO zeolite membrane has a high Si atom/Al atommolar ratio, resulting in a zeolite membrane having a wide range ofapplications excellent in acid resistance and water resistance.

A preferable range of the amount of Al atom source (including theabove-described aluminosilicate zeolite and the other Al atom sources)to silicon (Si atoms) contained in a raw material mixture other than aseed crystal (Al atom/Si atom ratio) is usually 0.01 or more, andpreferably 0.02 or more, more preferably 0.04 or more, and furtherpreferably 0.06 or more, and is usually 1.0 or less, and preferably 0.5or less, more preferably 0.2 or less, and still more preferably 0.1 orless. By controlling the amount within this range, the content ofnitrogen atoms and alkali metal elements in the zeolite can be easilycontrolled within a preferable range of the present invention. In orderto increase the Al atom/Si atom ratio, the amount of a silicon atomsource used with respect to an aluminum atom source may be reduced, andon the other hand, in order to reduce the ratio, the amount of a siliconatom source used with respect to an aluminum atom source may beincreased.

In certain embodiments of the present invention (for example, inventionsB to E), when the Al atom/Si atom ratio is more than 1.0, the waterresistance and acid resistance of an obtained RHO zeolite membrane arelow, and the use as a zeolite membrane may be limited. When the Alatom/Si atom ratio is smaller than 0.01, it may be difficult to obtainan RHO zeolite membrane.

An atom source other than a silicon atom source or an aluminum atomsource, such as gallium (Ga), iron (Fe), boron (B), titanium (Ti),zirconium (Zr), tin (Sn), or zinc (Zn), may be included in an aqueousreaction mixture.

The kind of alkali used as an alkali source is not particularly limited,and an alkali metal hydroxide or an alkaline earth metal hydroxide canbe used.

The metal species of these metal hydroxides is usually sodium (Na),potassium (K), lithium (Li), rubidium (Rb), cesium (Cs), calcium (Ca),magnesium (Mg), strontium (Sr), or barium (Ba), preferably Na, K, or Cs,and more preferably Na or Cs. Two or more metal species of metal oxidesmay be used in combination, and specifically, it is preferable to use Naand Cs in combination.

Specific examples of the metal hydroxide that can be used include analkali metal hydroxide such as sodium hydroxide, potassium hydroxide,lithium hydroxide, rubidium hydroxide, or cesium hydroxide; and analkaline earth metal hydroxide such as calcium hydroxide, magnesiumhydroxide, strontium hydroxide, or barium hydroxide.

As an alkali source used in an aqueous reaction mixture, a hydroxide ionof a counter anion of an organic template described below can be used.

In crystallization of the zeolite according to the present invention,although an organic template (structure-directing agent) is notnecessarily required, by using an organic template of a kindcorresponding to each structure, the ratio of silicon atoms to aluminumatoms of crystallized zeolite is increased and the crystallinity isimproved, and therefore, it is preferable to use an organic template.

The organic template may be any kind as long as the template can form adesired zeolite membrane. One kind of template may be used, or two ormore kinds thereof may be used in combination.

The kind of organic template suitable for reactions varies depending onthe zeolite structure to be synthesized, and an organic template thatprovides a desired zeolite structure may be used. Specifically, forexample, 18-crown-6-ether may be used for the RHO structure.

When the organic template is a cation, the template is accompanied by ananion that does not harm formation of zeolite. Representative examplesof such an anion include a halogen ion such as Cl⁻, Br⁻, or I⁻, and ahydroxide ion, an acetate, a sulfate, and a carboxylate. Among these, ahydroxide ion is particularly preferably used, and in the case of ahydroxide ion, the ion functions as an alkali source as described above.

The ratio of a Si atom source to an organic template in an aqueousreaction mixture in terms of the molar ratio of the organic template toSiO₂ (organic template/SiO₂ ratio) is usually 0.005 or more, andpreferably 0.01 or more, more preferably 0.02 or more, still morepreferably 0.05 or more, particularly preferably 0.08 or more, and mostpreferably 0.1 or more, and usually the ratio is 1 or less, andpreferably 0.5 or less, more preferably 0.4 or less, still morepreferably 0.35 or less, particularly preferably 0.30 or less, and mostpreferably 0.25 or less. When the organic template/SiO₂ ratio of anaqueous reaction mixture is in this range, zeolite that not only canform a dense zeolite membrane, but also has excellent acid resistanceand does not easily desorb Al atoms is obtained. Under these conditions,a particularly dense and excellent acid-resistant RHO aluminosilicatezeolite can be formed.

By using an appropriate amount of an alkali metal atom source, anorganic structure-directing agent described below can be easilycoordinated to aluminum in a suitable state, and therefore, a crystalstructure can be easily formed. The molar ratio (R/Si atom) of an alkalimetal atom source (R) and a silicon (Si atom) contained in the rawmaterial mixture for hydrothermal synthesis other than seed crystals isusually 0.1 or more, and preferably 0.15 or more, more preferably 0.20or more, still more preferably 0.25 or more, especially preferably 0.30or more, and particularly preferably 0.35 or more, and the ratio isusually 2.0 or less, and preferably 1.5 or less, more preferably 1.0 orless, still more preferably 0.8 or less, particularly preferably 0.6 orless, and most preferably 0.5 or less.

When the molar ratio of the alkali metal atom source to silicon (R/Siatom) is larger than the above-described upper limit, produced zeoliteis likely to be dissolved, and the zeolite may not be obtained or theyield may be considerably reduced. When the R/Si atom is smaller thanthe lower limit, the raw material Al atom source or Si atom source isnot sufficiently dissolved, a uniform raw material mixture forhydrothermal synthesis may not be obtained, and RHO zeolite may bedifficult to produce.

(Amount of Water)

The amount of water in a raw material mixture for hydrothermal synthesisin terms of a molar ratio to silicon (Si atoms) contained in the rawmaterial mixture other than a seed crystal is usually 10 or more, andpreferably 20 or more, more preferably 30 or more, still more preferably40 or more, and particularly preferably 50 or more, and usually is 200mol or less, and preferably 150 or less, more preferably 100 or less,still more preferably 80 or less, and particularly preferably 60 orless. When the amount is larger than the above-described upper limit,too dilute a reaction mixture may make it difficult to form a densemembrane without defects. When the amount is less than 10, due to athick reaction mixture, a spontaneous nucleus is likely to be generated,and growth of RHO zeolite from a support may be inhibited, which maymake it difficult to form a dense membrane.

(Seed Crystal)

In the present invention, a seed crystal may be used as one component ofa “zeolite” production raw material (raw material compound).

In hydrothermal synthesis, although not always necessary to have a seedcrystal in a reaction system, presence of a seed crystal can promotecrystallization of zeolite on a porous support. A method for allowing aseed crystal to exist in a reaction system is not particularly limited,and a method for adding a seed crystal in an aqueous reaction mixture ora method for depositing a seed crystal on a support can be used as insynthesis of powder zeolite. In the present invention, depositing a seedcrystal on a support is preferred. By depositing a seed crystal inadvance on a support, a dense zeolite membrane with high separationperformance can be easily formed.

A seed crystal to be used is not particularly limited as long as theseed is a zeolite that promotes crystallization, and for efficientcrystallization, a seed crystal having the same crystal type as azeolite membrane to be formed is preferable. For example, when forming azeolite membrane of RHO aluminosilicate, it is preferable to use a seedcrystal of RHO zeolite.

The seed crystal particle size is desirably close to the pore diameterof a support, and may be used after pulverization as necessary. Theparticle size is usually 20 nm or more, and preferably 50 nm or more,more preferably 100 nm or more, still more preferably 0.15 μm or more,particularly preferably 0.5 μm or more, and most preferably 0.7 μm ormore, and usually 5 μm or less, and preferably 3 μm or less, morepreferably 2 μm or less, and particularly preferably 1.5 μm or less.

Depending on the pore diameter of a support, it may be desirable for theparticle size of the seed crystal to be small, and a seed crystal may becrushed and used as necessary. The particle diameter of a seed crystalis usually 5 nm or more, and preferably 10 nm or more, and morepreferably 20 nm or more, and is usually 5 μm or less, preferably 3 μmor less, and more preferably 2 μm or less.

The method for depositing a seed crystal on a support is notparticularly limited, and for example, a dip method in which a seedcrystal is dispersed in a solvent such as water and a support isimmersed in the dispersion to deposit the seed crystal on the surface; asuction method in which, after immersing a support with one end sealedin a dispersion in which a seed crystal is dispersed in a solvent suchas water, the support is sucked from the other end in such a manner thatthe seed crystal is firmly deposited on the surface of the support; amethod of applying a slurry obtained by mixing a seed crystal with asolvent such as water onto a support; or the like can be used. A dipmethod and a suction method are desirable for producing a zeolitemembrane with favorable reproducibility by controlling the amount ofseed crystals deposited, and from the viewpoint of bringing a seedcrystal into close contact with a support, a method of applying the seedcrystal on a slurry onto the support and a suction method are desirable.For the purpose of closely depositing a seed crystal on a support and/orfor the purpose of removing excessive seed crystal, it is alsopreferable to rub and push the support on which the seed crystal isdeposited with a finger wearing a latex glove following the dip methodor the suction method.

A solvent for dispersing a seed crystal is not particularly limited, andwater or an alkaline aqueous solution is particularly preferable.Although the kind of alkaline aqueous solution is not specificallylimited, a sodium hydroxide aqueous solution or a potassium hydroxideaqueous solution is preferable. These alkali species may be mixed. Thealkali concentration of an alkaline aqueous solution is not particularlylimited, and is usually 0.0001% by mole or more, and preferably 0.0002%by mole or more, more preferably 0.001% by mole or more, and furtherpreferably 0.002% by mole or more. The concentration is usually 1% bymole or less, and preferably 0.8% by mole or less, more preferably 0.5%by mole or less, and still more preferably 0.2% by mole or less.

A solvent for dispersing a seed crystal is not particularly limited, andwater is particularly preferable. The amount of a seed crystal to bedispersed is not particularly limited, and is, based on the total weightof the dispersion, usually 0.05% by mass or more, and preferably 0.1% bymass or more, more preferably 0.5% by mass or more, still morepreferably 1% by mass or more, particularly preferably 2% by mass ormore, and most preferably 3.0% by mass or more. The amount is usually20% by mass or less, and preferably 10% by mass or less, more preferably5% by mass or less, and still more preferably 4% by mass or less.

When the amount of a seed crystal to be dispersed is too small, sincethe amount of the seed crystal deposited on a support is small, aportion where no zeolite is generated on the support during hydrothermalsynthesis is partially formed, which may result in a defective membrane.On the other hand, for example, the amount of a seed crystal depositedon a porous support by a dip method is almost constant when the amountof the seed crystal in a dispersion is more than a certain amount, andtherefore, when the amount of the seed crystal in the dispersion is toolarge, the seed crystal is, wasted, which is disadvantageous in terms ofcost.

It is desirable to form a zeolite membrane after drying a seed crystalafter depositing the seed crystal on a support by dipping, suction orslurry application. Drying temperature is usually 50° C. or higher, andpreferably 80° C. or higher, and more preferably 100° C. or higher, andis usually 200° C. or lower, and preferably 180° C. or lower, and morepreferably 150° C. or lower. As long as the drying is sufficientlyperformed, there is no problem with any drying time, and the drying timeis usually 10 minutes or more, and preferably 30 minutes or more, andthe upper limit is not specified, and is usually 5 hours or less from aneconomic viewpoint.

For a dried seed crystal support, for the purpose of depositing the seedcrystal on the support and/or for the purpose of removing excess seedcrystal, it is also preferable to rub and push the support on which theseed crystal is deposited with a finger wearing a latex glove.

The amount of a seed crystal to be preliminarily deposited on a poroussupport is not particularly limited, and is, by mass per 1 m² of thefilm-forming surface of the porous support, usually 0.1 g or more, andpreferably 0.3 g or more, more preferably 0.5 g or more, furtherpreferably 0.80 g or more, and most preferably 1.0 g or more, andusually 100 g or less, and preferably 50 g or less, more preferably 10 gor less, still more preferably 8 g or less, and most preferably 5 g orless.

When the amount of a seed crystal deposited is less than theabove-described lower limit, a crystal is less likely to be formed, andthe membrane growth tends to be insufficient, or the membrane growthtends to be uneven. When the amount of a seed crystal is higher than theabove-described upper limit, the surface irregularities may be increasedby the seed crystal, or a seed crystal falling from a support may easilycause a spontaneous nucleus to grow and inhibit membrane growth on thesupport. In either case, there is a tendency that a dense zeolitemembrane is less likely to be generated.

When a zeolite membrane is formed on a porous support by hydrothermalsynthesis, there is no particular limitation on a method of immobilizinga support, and the support may be fixed in any form such as verticallyor horizontally. In this case, a zeolite membrane may be formed by astationary method, or a zeolite membrane may be formed under stirring ofan aqueous reaction mixture.

Hydrothermal synthesis is carried out by placing a support supporting aseed crystal as described above and a prepared mixture for hydrothermalsynthesis or an aqueous gel obtained by aging this in a pressure vesseland maintaining a predetermined temperature under stirring, whilerotating or swinging the container, or in a stationary state, under aself-generated pressure or under gas pressurization that does notinhibit crystallization. Hydrothermal synthesis in a stationary state isdesirable in that the synthesis does not inhibit crystal growth from aseed crystal on a support.

The reaction temperature at the time of forming a zeolite membrane byhydrothermal synthesis is not particularly limited as long as thetemperature is a temperature suitable for obtaining a membrane having atarget zeolite structure, and is usually 100° C. or higher, andpreferably 110° C. or higher, further preferably 120° C. or higher,especially preferably 130° C. or higher, particularly preferably 140° C.or higher, and most preferably 150° C. or higher, and is usually 200° C.or lower, preferably 190° C. or lower, more preferably 180° C. or lower,and further preferably 170° C. or lower. When the reaction temperatureis too low, zeolite may be difficult to crystallize. When the reactiontemperature is too high, zeolite of a type different from target zeolitemay be easily generated.

The heating (reaction) time for forming a zeolite membrane byhydrothermal synthesis is not particularly limited, and may be any timesuitable for obtaining a membrane having target zeolite structure, andis usually 3 hours or more, and preferably 8 hours or more, morepreferably 12 hours or more, and particularly preferably 15 hours ormore, and is usually 10 days or less, and preferably 5 days or less,more preferably 3 days or less, still more preferably 2 days or less,and particularly preferably 1.5 days or less. When the reaction time istoo short, zeolite may be difficult to crystallize. When the reactiontime is too long, zeolite of a type different from target zeolite may beeasily formed.

The pressure at the time of hydrothermal synthesis is not particularlylimited, and a self-generated pressure generated when an aqueousreaction mixture placed in a closed vessel is heated to theabove-described temperature range is sufficient. If necessary, an inertgas such as nitrogen may be added.

It is also possible to improve the denseness of a zeolite membrane byrepeating hydrothermal synthesis a plurality of times. When hydrothermalsynthesis is repeated a plurality of times, a zeolite membrane compositeobtained by the first hydrothermal synthesis may be washed with water,dried by heating, and then immersed again in a newly prepared aqueousreaction mixture for hydrothermal synthesis. Although the zeolitemembrane composite obtained after the first hydrothermal synthesis doesnot necessarily need to be washed with water or dried, the aqueousreaction mixture can be kept at an intended composition by washing withwater and drying. In the case of performing synthesis a plurality oftimes, the number of the synthesis is usually 2 times or more, andusually 10 times or less, preferably 5 times or less, and morepreferably 3 times or less. The washing with water may be performed onceor repeated a plurality of times.

A zeolite membrane composite obtained by hydrothermal synthesis iswashed with water, then heated and dried. Here, the heat treatment meansthat a zeolite membrane composite is dried by applying heat, and when anorganic template is used, the organic template is fired and removed.

For the purpose of drying, the temperature of the heat treatment isusually 50° C. or higher, and preferably 80° C. or higher, and morepreferably 100° C. or higher, and usually 200° C. or lower, andpreferably 150° C. or lower. For the purpose of firing and removing theorganic template, the temperature of the heat treatment is usually 250°C. or higher, and preferably 300° C. or higher, more preferably 350° C.or higher, and still more preferably 400° C. or higher, and is usually800° C. or lower, and preferably 600° C. or lower, further preferably550° C. or lower, and particularly preferably 500° C. or lower.

For the purpose of firing and removing an organic template, when thetemperature of the heat treatment is too low, the residual ratio of theorganic template tends to increase, and pores of zeolite decrease, whichmay reduce the permeation amount when used for ammonia separation. Whenthe heat treatment temperature is too high, since the difference inthermal expansion coefficient between a support and zeolite becomeslarge, a crack may easily occur in a zeolite membrane, and the densenessof the zeolite membrane may be lost and the separation performance maybe lowered.

The time for the heat treatment is not particularly limited as long as azeolite membrane is sufficiently dried and an organic template is firedand removed, and for the purpose of drying, the time is preferably 0.5hours or more, and more preferably 1 hour or more, and in order toremove an organic template by firing, although the time varies dependingon the temperature rise rate or the temperature fall rate, the time ispreferably 1 hour or longer, and more preferably 5 hours or longer. Theupper limit of the heating time is not particularly limited, and isusually 200 hours or less, and preferably 150 hours or less, and morepreferably 100 hours or less.

For the purpose of firing a template, the heat treatment may beperformed in an air atmosphere, and may also be performed in anatmosphere to which an inert gas such as nitrogen or oxygen is added.

When hydrothermal synthesis is performed in the presence of an organictemplate, after an obtained zeolite membrane composite is washed withwater, it is appropriate to remove the organic template preferably bythe above-described heat treatment or firing, for example, by heattreatment or extraction.

The temperature rise rate during a heat treatment for the purpose offiring and removing an organic template is desirably as slow as possiblein order to prevent a zeolite membrane from cracking due to thedifference in thermal expansion coefficient between a porous support andzeolite. The temperature rise rate is usually 5° C./min or less, andpreferably 2° C./min or less, more preferably 1° C./min or less, furtherpreferably 0.5° C./min or less, and particularly preferably 0.3° C./minor less. The lower limit of the temperature rise rate is usually 0.1°C./min or more in consideration of workability.

In a heat treatment for the purpose of firing and removing an organictemplate, it is necessary to control the temperature drop rate after theheat treatment in order to avoid a crack in a zeolite membrane, and thetemperature drop rate is preferably as slow as the temperature riserate. The temperature drop rate is usually 5° C./min or less, andpreferably 2° C./min or less, more preferably 1° C./min or less, furtherpreferably 0.5° C./min or less, and particularly preferably 0.3° C./minor less. The lower limit of the temperature drop rate is usually 0.1°C./min or more in consideration of workability.

<Method for Producing MFI Zeolite Membrane> (Silicon Atom Source)

Examples a silicon (Si) atom source which can be used in an aqueousreaction mixture include aluminosilicate zeolite, fumed silica,colloidal silica, amorphous silica, a silicon alkoxide such as sodiumsilicate, methyl silicate, ethyl silicate, or trimethylethoxysilane,tetraethyl orthosilicate, and aluminosilicate gel. Preferred examplesthereof include aluminosilicate zeolite, fumed silica, colloidal silica,amorphous silica, sodium silicate, methyl silicate, ethyl silicate,silicon alkoxide, and aluminosilicate gel. These may be used singly orin combination of two or more kinds thereof.

A Si atom source is used in such a manner that the amount of other rawmaterials used with respect to the Si atom source is within the above-or below-described preferred range.

(Aluminum Atom Source)

An aluminum (Al) atom source used for producing a porous support-MFIzeolite membrane composite is not particularly limited, and examplesthereof include aluminosilicate zeolite, amorphous aluminum hydroxide,aluminum hydroxide with gibbsite structure, aluminum hydroxide withbayerite structure, aluminum nitrate, aluminum sulfate, aluminum oxide,sodium aluminate, boehmite, pseudoboehmite, aluminum alkoxide, andaluminosilicate gel. Amorphous aluminum hydroxide, sodium aluminate,boehmite, pseudoboehmite, aluminum alkoxide, and aluminosilicate gel arepreferable, and amorphous aluminum hydroxide, sodium aluminate, andaluminosilicate gel are particularly preferable. These may be usedsingly or in combination of two or more kinds thereof.

A preferable range of the amount of aluminum atom source (including theabove-described aluminosilicate zeolite and the other aluminum atomsources) to silicon (Si atoms) contained in a raw material mixture otherthan a seed crystal (Al atom/Si atom ratio) as a molar ratio is usually0.001 or more, and preferably 0.002 or more, more preferably 0.003 ormore, and further preferably 0.004 or more, and is usually 1.0 or less,and preferably 0.5 or less, more preferably 0.2 or less, and still morepreferably 0.1 or less. By controlling the amount within this range, thecontent of nitrogen atoms and alkali metal elements in the zeolite canbe easily controlled within a preferable range of the present invention.In order to increase the Al atom/Si atom ratio, the amount of a siliconatom source used with respect to an aluminum atom source may be reduced,and on the other hand, in order to reduce the ratio, the amount of asilicon atom source used with respect to an aluminum atom source may beincreased.

An atom source other than a Si atom source or an Al atom source, such asGa, Fe, B, Ti, Zr, Sn, or Zn, may be included in an aqueous reactionmixture.

The kind of alkali used as an alkali source is not particularly limited,and an alkali metal hydroxide or an alkaline earth metal hydroxide canbe used.

Specific examples of the metal hydroxide that can be used include analkali metal hydroxide such as sodium hydroxide, potassium hydroxide,lithium hydroxide, rubidium hydroxide, or cesium hydroxide; and analkaline earth metal hydroxide such as calcium hydroxide, magnesiumhydroxide, strontium hydroxide, or barium hydroxide.

As an alkali source used in an aqueous reaction mixture, a hydroxide ionof a counter anion of an organic template described below can be used.

In crystallization of the zeolite according to the present invention,although an organic template (structure-directing agent) is notnecessarily required, by using an organic template of a kindcorresponding to each structure, the ratio of silicon atoms to aluminumatoms of crystallized zeolite is increased and the crystallinity isimproved, and therefore, it is preferable to use an organic template.

The organic template may be any kind as long as the template can form adesired zeolite membrane. One kind of template may be used, or two ormore kinds thereof may be used in combination.

The kind of organic template suitable for reactions varies depending onthe zeolite structure to be synthesized, and an organic template thatprovides a desired zeolite structure may be used. Specifically, forexample, tetrapropylammonium hydroxide may be used for the MFIstructure.

When the organic template is a cation, the template is accompanied by ananion that does not harm formation of zeolite. Representative examplesof such an anion include a halogen ion such as Cl⁻, Br⁻, or I⁻, and ahydroxide ion, an acetate, a sulfate, and a carboxylate. Among these, ahydroxide ion is particularly preferably used, and in the case of ahydroxide ion, the ion functions as an alkali source as described above.

The ratio of a Si atom source to an organic template in an aqueousreaction mixture in terms of the molar ratio of the organic template toSiO₂ (organic template/SiO₂ ratio) is usually 0.005 or more, andpreferably 0.01 or more, more preferably 0.02 or more, especially 0.05or more, and most preferably 0.1 or more, and usually the ratio is 1 orless, and preferably 0.5 or less, more preferably 0.3 or less,especially 0.25 or less, and particularly preferably 0.20 or less. Whenthe organic template/SiO₂ ratio of an aqueous reaction mixture is inthis range, zeolite that not only can form a dense zeolite membrane, butalso has excellent acid resistance and does not easily desorb Al isobtained. Under these conditions, a particularly dense and excellentacid-resistant MFI aluminosilicate zeolite can be formed.

By using an appropriate amount of an alkali metal atom source, anorganic structure-directing agent described below can be easilycoordinated to aluminum in a suitable state, and therefore, a crystalstructure can be easily formed. The molar ratio (R/Si) of an alkalimetal atom source (R) and a silicon (Si) contained in the raw materialmixture for hydrothermal synthesis other than seed crystals is usually0.01 or more, and preferably 0.02 or more, more preferably 0.03 or more,still more preferably 0.04 or more, and particularly preferably 0.05 ormore, and the ratio is usually 1.0 or less, and preferably 0.6 or less,more preferably 0.4 or less, still more preferably 0.2 or less, andparticularly preferably 0.1 or less.

When the molar ratio of the alkali metal atom source to silicon (R/Si)is larger than the above-described upper limit, produced zeolite islikely to be dissolved, and the zeolite may not be obtained or the yieldmay be considerably reduced. When the R/Si is smaller than the lowerlimit, the raw material Al atom source or Si atom source is notsufficiently dissolved, a uniform raw material mixture for hydrothermalsynthesis may not be obtained, and MFI zeolite may be difficult toproduce.

(Amount of Water)

The amount of water in a raw material mixture for hydrothermal synthesisin terms of a molar ratio to silicon (Si) contained in the raw materialmixture other than a seed crystal is usually 10 or more, and preferably15 or more, more preferably 20 or more, still more preferably 25 ormore, and particularly preferably 30 or more, and usually is 500 mol orless, and preferably 300 or less, more preferably 200 or less, stillmore preferably 150 or less, and particularly preferably 100 or less.When the amount is larger than the above-described upper limit, toodilute a reaction mixture may make it difficult to form a dense membranewithout defects. When the amount is less than 10, due to a thickreaction mixture, a spontaneous nucleus is likely to be generated, andgrowth of MFI zeolite from a support may be inhibited, which may make itdifficult to form a dense membrane.

(Seed Crystal)

In the present invention, a seed crystal may be used as one component ofa “zeolite” production raw material (raw material compound).

In hydrothermal synthesis, although not always necessary to have a seedcrystal in a reaction system, presence of a seed crystal can promotecrystallization of zeolite on a porous support. A method for allowing aseed crystal to exist in a reaction system is not particularly limited,and a method for adding a seed crystal in an aqueous reaction mixture ora method for depositing a seed crystal on a support can be used as insynthesis of powder zeolite. In the present invention, depositing a seedcrystal on a support is preferred. By depositing a seed crystal inadvance on a support, a dense zeolite membrane with high separationperformance can be easily formed.

A seed crystal to be used is not particularly limited as long as theseed is a zeolite that promotes crystallization, and for efficientcrystallization, a seed crystal having the same crystal type as azeolite membrane to be formed is preferable. For example, when forming azeolite membrane of MFI aluminosilicate, it is preferable to use a seedcrystal of MFI zeolite.

The seed crystal particle size is desirably close to the pore diameterof a support, and may be used after pulverization as necessary. Theparticle size is usually 1 nm or more, and preferably 10 nm or more,more preferably 50 nm or more, still more preferably 0.1 μm or more,particularly preferably 0.5 μm or more, especially preferably 0.7 μm ormore, and most preferably 1 μm or more, and usually 5 μm or less, andpreferably 3 μm or less, more preferably 2 μm or less, most preferably1.5 μm or less, and particularly preferably 1.2 μm or less.

Depending on the pore diameter of a support, it may be desirable for theparticle size of the seed crystal to be small, and a seed crystal may becrushed and used as necessary. The particle diameter of a seed crystalis usually 0.5 nm or more, and preferably 1 nm or more, and morepreferably 2 nm or more, and is usually 5 μm or less, preferably 3 μm orless, and more preferably 2 μm or less.

The method for depositing a seed crystal on a support is notparticularly limited, and for example, a dip method in which a seedcrystal is dispersed in a solvent such as water and a support isimmersed in the dispersion to deposit the seed crystal on the surface; asuction method in which, after immersing a support with one end sealedin a dispersion in which a seed crystal is dispersed in a solvent suchas water, the support is sucked from the other end in such a manner thatthe seed crystal is firmly deposited on the surface of the support; amethod of applying a slurry obtained by mixing a seed crystal with asolvent such as water onto a support; or the like can be used. A dipmethod and a suction method are desirable for producing a zeolitemembrane with favorable reproducibility by controlling the amount ofseed crystals deposited, and from the viewpoint of bringing a seedcrystal into close contact with a support, a method of applying the seedcrystal on a slurry onto the support and a suction method are desirable.For the purpose of closely depositing a seed crystal on a support and/orfor the purpose of removing excessive seed crystal, it is alsopreferable to rub and push the support on which the seed crystal isdeposited with a finger wearing a latex glove following the dip methodor the suction method.

A solvent for dispersing a seed crystal is not particularly limited, andwater or an alkaline aqueous solution is particularly preferable.Although the kind of alkaline aqueous solution is not specificallylimited, a sodium hydroxide aqueous solution or a potassium hydroxideaqueous solution is preferable. These alkali species may be mixed. Thealkali concentration of an alkaline aqueous solution is not particularlylimited, and is usually 0.0001% by mole or more, and preferably 0.0002%by mole or more, more preferably 0.001% by mole or more, and furtherpreferably 0.002% by mole or more. The concentration is usually 1% bymole or less, and preferably 0.8% by mole or less, more preferably 0.5%by mole or less, and still more preferably 0.2% by mole or less.

A solvent for dispersing a seed crystal is not particularly limited, andwater is particularly preferable. The amount of a seed crystal to bedispersed is not particularly limited, and is, based on the total weightof the dispersion, usually 0.05% by mass or more, and preferably 0.1% bymass or more, more preferably 0.5% by mass or more, still morepreferably 1% by mass or more, particularly preferably 2% by mass ormore, and most preferably 3% by mass or more. The amount is usually 20%by mass or less, and preferably 10% by mass or less, more preferably 5%by mass or less, and still more preferably 4% by mass or less.

When the amount of a seed crystal to be dispersed is too small, sincethe amount of the seed crystal deposited on a support is small, aportion where no zeolite is generated on the support during hydrothermalsynthesis is partially formed, which may result in a defective membrane.On the other hand, for example, the amount of a seed crystal depositedon a porous support by a dip method is almost constant when the amountof the seed crystal in a dispersion is more than a certain amount, andtherefore, when the amount of the seed crystal in the dispersion is toolarge, the seed crystal is wasted, which is disadvantageous in terms ofcost.

It is desirable to form a zeolite membrane after drying a seed crystalafter depositing the seed crystal on a support by dipping, suction orslurry application. Drying temperature is usually 50° C. or higher, andpreferably 80° C. or higher, and more preferably 100° C. or higher, andis usually 200° C. or lower, and preferably 180° C. or lower, and morepreferably 150° C. or lower. As long as the drying is sufficientlyperformed, there is no problem with any drying time, and the drying timeis usually 10 minutes or more, and preferably 30 minutes or more, andthe upper limit is not specified, and is usually 5 hours or less from aneconomic viewpoint.

For a dried seed crystal support, for the purpose of depositing the seedcrystal on the support and/or for the purpose of removing excess seedcrystal, it is also preferable to rub and push the support on which theseed crystal is deposited with a finger wearing a latex glove.

The amount of a seed crystal to be preliminarily deposited on a poroussupport is not particularly limited, and is, by mass per 1 m² of thefilm-forming surface of the porous support, usually 0.1 g or more, andpreferably 0.3 g or more, more preferably 0.5 g or more, furtherpreferably 0.80 g or more, and most preferably 1.0 g or more, andusually 100 g or less, and preferably 50 g or less, more preferably 10 gor less, still more preferably 8 g or less, and most preferably 5 g orless.

When the amount of a seed crystal deposited is less than theabove-described lower limit, a crystal is less likely to be formed, andthe membrane growth tends to be insufficient, or the membrane growthtends to be uneven. When the amount of a seed crystal is higher than theabove-described upper limit, the surface irregularities may be increasedby the seed crystal, or a seed crystal falling from a support may easilycause a spontaneous nucleus to grow and inhibit membrane growth on thesupport. In either case, there is a tendency that a dense zeolitemembrane is less likely to be generated.

When a zeolite membrane is formed on a porous support by hydrothermalsynthesis, there is no particular limitation on a method of immobilizinga support, and the support may be fixed in any form such as verticallyor horizontally. In this case, a zeolite membrane may be formed by astationary method, or a zeolite membrane may be formed under stirring ofan aqueous reaction mixture.

Hydrothermal synthesis is carried out by placing a support supporting aseed crystal as described above and a prepared mixture for hydrothermalsynthesis or an aqueous gel obtained by aging this in a pressure vesseland maintaining a predetermined temperature under stirring, whilerotating or swinging the container, or in a stationary state, under aself-generated pressure or under gas pressurization that does notinhibit crystallization. Hydrothermal synthesis in a stationary state isdesirable in that the synthesis does not inhibit crystal growth from aseed crystal on a support.

The reaction temperature at the time of forming a zeolite membrane byhydrothermal synthesis is not particularly limited as long as thetemperature is a temperature suitable for obtaining a membrane having atarget zeolite structure, and is usually 100° C. or higher, andpreferably 120° C. or higher, further preferably 130° C. or higher,especially preferably 140° C. or higher, particularly preferably 150° C.or higher, and most preferably 160° C. or higher, and is usually 200° C.or lower, preferably 190° C. or lower, further preferably 180° C. orlower, and particularly preferably 170° C. or lower. When the reactiontemperature is too low, zeolite may be difficult to crystallize. Whenthe reaction temperature is too high, zeolite of a type different fromtarget zeolite may be easily generated.

The heating (reaction) time for forming a zeolite membrane byhydrothermal synthesis is not particularly limited, and may be any timesuitable for obtaining a membrane having target zeolite structure, andis usually 1 hour or more, and preferably 5 hours or more, and furtherpreferably 10 hours or more, and is usually 10 days or less, andpreferably 5 days or less, more preferably 3 days or less, still morepreferably 2 days or less, and particularly preferably 1 day or less.When the reaction time is too short, zeolite may be difficult tocrystallize. When the reaction time is too long, zeolite of a typedifferent from target zeolite may be easily formed.

The pressure at the time of hydrothermal synthesis is not particularlylimited, and a self-generated pressure generated when an aqueousreaction mixture placed in a closed vessel is heated to theabove-described temperature range is sufficient. If necessary, an inertgas such as nitrogen may be added.

It is also possible to improve the denseness of a zeolite membrane byrepeating hydrothermal synthesis a plurality of times. When hydrothermalsynthesis is repeated a plurality of times, a zeolite membrane compositeobtained by the first hydrothermal synthesis may be washed with water,dried by heating, and then immersed again in a newly prepared aqueousreaction mixture for hydrothermal synthesis. Although the zeolitemembrane composite obtained after the first hydrothermal synthesis doesnot necessarily need to be washed with water or dried, the aqueousreaction mixture can be kept at an intended composition by washing withwater and drying. In the case of performing synthesis a plurality oftimes, the number of the synthesis is usually 2 times or more, andusually 10 times or less, preferably 5 times or less, and morepreferably 3 times or less. The washing with water may be performed onceor a plurality of times.

A zeolite membrane composite obtained by hydrothermal synthesis iswashed with water, then heated and dried. Here, the heat treatment meansthat a zeolite membrane composite is dried by applying heat, and when anorganic template is used, the organic template is fired and removed.

For the purpose of drying, the temperature of the heat treatment isusually 50° C. or higher, and preferably 80° C. or higher, and morepreferably 100° C. or higher, and usually 200° C. or lower, andpreferably 150° C. or lower. For the purpose of firing and removing theorganic template, the temperature of the heat treatment is usually 350°C. or higher, and preferably 400° C. or higher, more preferably 450° C.or higher, and still more preferably 500° C. or higher, and is usually900° C. or lower, and preferably 800° C. or lower, further preferably700° C. or lower, and particularly preferably 600° C. or lower.

For the purpose of firing and removing an organic template, when thetemperature of the heat treatment is too low, the residual ratio of theorganic template tends to increase, and pores of zeolite decrease, whichmay reduce the permeation amount when used for ammonia separation. Whenthe heat treatment temperature is too high, since the difference inthermal expansion coefficient between a support and zeolite becomeslarge, a crack may easily occur in a zeolite membrane, and the densenessof the zeolite membrane may be lost and the separation performance maybe lowered. When tetrapropylammonium hydroxide is used as an organictemplate, the content of nitrogen atoms in zeolite can be controlled byadjusting the heat treatment temperature.

The time for the heat treatment is not particularly limited as long as azeolite membrane is sufficiently dried and an organic template is firedand removed, and for the purpose of drying, the time is preferably 0.5hours or more, and more preferably 1 hour or more, and in order toremove an organic template by firing, although the time varies dependingon the temperature rise rate or the temperature fall rate, the time ispreferably 1 hour or longer, and more preferably 5 hours or longer. Theupper limit of the heating time is not particularly limited, and isusually 200 hours or less, and preferably 150 hours or less, and morepreferably 100 hours or less.

For the purpose of firing a template, the heat treatment may beperformed in an air atmosphere, and may also be performed in anatmosphere to which an inert gas such as nitrogen or oxygen is added.

When hydrothermal synthesis is performed in the presence of an organictemplate, after an obtained zeolite membrane composite is washed withwater, it is appropriate to remove the organic template preferably bythe above-described heat treatment or firing, for example, by heattreatment or extraction.

The temperature rise rate during a heat treatment for the purpose offiring and removing an organic template is desirably as slow as possiblein order to prevent a zeolite membrane from cracking due to thedifference in thermal expansion coefficient between a porous support andzeolite. The temperature rise rate is usually 5° C./min or less, andpreferably 2° C./min or less, more preferably 1° C./min or less,particularly preferably 0.5° C./min or less, and most preferably 0.3°C./min or less. The lower limit of the temperature rise rate is usually0.1° C./min or more in consideration of workability.

In a heat treatment for the purpose of firing and removing an organictemplate, it is necessary to control the temperature drop rate after theheat treatment in order to avoid a crack in a zeolite membrane, and thetemperature drop rate is preferably as slow as the temperature riserate. The temperature drop rate is usually 5° C./min or less, andpreferably 2° C./min or less, more preferably 1° C./min or less,particularly preferably 0.5° C./min or less, and most preferably 0.3°C./min or less. The lower limit of the temperature drop rate is usually0.1° C./min or more in consideration of workability.

(Ion Exchange) A synthesized zeolite membrane may be ion exchanged asnecessary. In particular, in certain embodiments of the presentinvention (for example, zeolite membranes of Inventions B, C, D, and E),the synthesized zeolite membrane undergoes an ion exchange treatment.Since the thermal expansion characteristics and the separation heatstability of ammonia of zeolite, which are one of the characteristics ofthe present invention, are greatly affected by the cationic species inthe zeolite, this ion exchange is an important control method. As willbe described below, the ammonia permeation performance and/or separationperformance of a zeolite membrane may be improved depending on thecationic species to be used. In other words, the cationic species usedin the present invention is appropriately selected in consideration ofthe ammonia permeation performance and separation performance whileensuring the thermal expansion characteristics and the ammoniaseparation heat stability of the above zeolite.

(Ion Exchange)

When a zeolite membrane is synthesized using an organic template, ionexchange is usually performed after removing the organic template. Inthe present invention, in order to increase the nitrogen content of azeolite membrane surface, NH₄ ⁺, any cationic species obtained byprotonating an organic amine having from 1 to 20 carbon atoms, such asmethylamine, dimethylamine, trimethylamine, ethylamine, diethylamine,triethylamine, ethylenediamine, dimethylethylenediamine,tetramethylethylenediamine, diethylenetriamine, triethylenetetraamine,aniline, methylaniline, benzylamine, methylbenzylamine,hexamethylenediamine, N,N-diisopropylethylamine,N,N,N-trimethyl-1-adamantanamine, pyridine, or piperidine is preferableas an ion for ion exchange, and an alkali metal ion such as proton, Na⁺,K⁺, Li⁺, Rb⁺, or Cs⁺, an alkaline earth metal ion such as Ca²⁺, Mg²⁺,Sr²⁺, or Ba²⁺, a transition metal ion such as Fe, Cu, Zn, Ga, or La, orthe like may coexist. Among these, a proton, NH₄ ⁺, Na⁺, Li⁺, Cs⁺, an Feion, a Ga ion, or an La ion is preferable. A plurality of kinds of theseions may be mixed in zeolite, and a method of mixing the above-describedions is suitably employed in order to balance the thermal expansioncharacteristics and the ammonia permeation performance of the zeolite.By controlling the cationic species to be ion-exchanged and the amountthereof as described above, the ammonia affinity of the zeolite and theeffective pore diameter in the zeolite pores can be controlled, wherebyit is possible to increase the ammonia permeation selectivity and toimprove the permeation amount of ammonia. Among these, NH₄ ⁺, anycationic species obtained by protonating an organic amine having from 1to 20 carbon atoms, such as methylamine, dimethylamine, trimethylamine,ethylamine, diethylamine, triethylamine, ethylenediamine,dimethylethylenediamine, tetramethylethylenediamine, diethylenetriamine,triethylenetetraamine, aniline, methylaniline, benzylamine,methylbenzylamine, hexamethylenediamine, N,N-diisopropylethylamine,N,N,N-trimethyl-1-adamantanamine, pyridine, or piperidine is preferableas an ionic species that increases the ammonia permeation selectivity.Among them, NH₄ ⁺ or a cationic species in which an amine with a smallmolecular size such as an organic amine having from 1 to 6 carbon atomsis protonated is more preferable for the above reason, and among them,NH₄ ⁺ is particularly preferable. On the other hand, as an ion speciesthat improves the permeation amount of ammonia, a proton, Na⁺, Li⁺, Cs⁺,an Fe ion, a Ga ion, or an La ion is preferable, an Na⁺ ion, an Li⁺ ion,or a Cs⁺ ion is particularly preferable, and an Na⁺ ion most preferablycoexists. In the present invention, the molar ratio of nitrogen atoms toAl atoms in a zeolite membrane can be controlled by adjusting theexchange amount of ions that essentially require ionic speciescontaining nitrogen atoms.

When Na⁺ ions are contained in the zeolite of the present invention, thecontent thereof in terms of molar ratio with respect to Al atoms in thezeolite is usually 0.01 or more, and preferably 0.02 or more, morepreferably 0.03 or more, still more preferably 0.04 or more, andparticularly preferably 0.05 or more, and the upper limit thereof is notparticularly limited, and is usually 0.10 molar equivalent or less, andpreferably 0.070 molar equivalent or less, more preferably 0.065 molarequivalent or less, further preferably 0.060 molar equivalent or less,and most preferably 055 molar equivalent or less. By using zeolitehaving a Na⁺/Al atomic ratio in such a specific region, ammonia can beseparated from a mixed gas composed of a plurality of componentsincluding ammonia and hydrogen and/or nitrogen with high permeability.

Ion exchange may be performed by treating a zeolite membrane afterfiring (for example, when using an organic template) with a nitrate, asulfate, a phosphate, an organic acid salt, a hydroxide, and a halogen(such as Cl or Br) salt of the above-described cation to beion-exchanged, and in some cases, an acid such as hydrochloric acid,usually at from room temperature to 100° C., followed by washing withwater or with hot water of from 40° C. to 100° C. A solvent used for anion exchange treatment may be water or an organic solvent as long as asalt to be ion-exchanged is dissolved, and the concentration of the saltto be treated is usually 10 mol/L or less, and the lower limit is 0.1mol/L or more, preferably 0.5 mol/L or more, and more preferably 1 mol/Lor more. These treatment conditions may be appropriately set accordingto the salt and solvent kind to be used. When an acid such ashydrochloric acid is used, the acid destroys the crystal structure ofzeolite, and therefore, the concentration of the acid to be treated isusually 5 mol/L or less, and the temperature and time may beappropriately set. Since the ion exchange rate increases by performingan ion exchange treatment repeatedly, the number of times of ionexchange treatments is not particularly limited, and the treatment maybe repeated until a desired effect is obtained. An ion-exchanged zeolitemembrane hinders gas permeability when a residue from a raw material foran ion exchange treatment is present in zeolite pores after the ionexchange treatment, and therefore, the zeolite membrane may be fired atfrom 200 to 500° C. and the residue after the ion exchange treatment maybe removed, as necessary.

(Nitrate Treatment)

In certain embodiments of the present invention (for example, zeolitemembranes of inventions B, C, D, and E), since it is preferable to use anitrate treatment as a method for adjusting the content of nitrogenatoms in a zeolite membrane, a nitrate treatment will be describedbelow.

In the present invention, a synthesized zeolite membrane may besubjected to a nitrate treatment as necessary. A nitrate treatment maybe performed after an organic template is removed by firing even in astate containing the organic template. A nitrate treatment is performed,for example, by immersing a zeolite membrane composite in a solutioncontaining nitrate. This may be preferable because an effect of anitrate blocking a fine defect present on the film surface may beobtained. Furthermore, when nitrate is present in zeolite pores, azeolite membrane has an effect of improving the affinity of the zeolitemembrane with ammonia, and this treatment is suitably employed as atechnique for improving the permeability of ammonia. A solvent used fora nitrate treatment may be water or an organic solvent as long as a saltdissolves, a nitrate to be used is not limited, and examples thereofinclude magnesium nitrate, calcium nitrate, barium nitrate, aluminumnitrate, gallium nitrate, indium nitrate, iron nitrate, cobalt nitrate,nickel nitrate, copper nitrate, and zinc nitrate. These may be usedsingly or in combination of two or more kinds thereof. Among these,magnesium nitrate, calcium nitrate, barium nitrate, aluminum nitrate,gallium nitrate, or indium nitrate is preferable, and among them,magnesium nitrate, calcium nitrate, barium nitrate, or aluminum nitrateis more preferable, and aluminum nitrate is particularly preferablebecause an effect of blocking a fine defect on the surface of a zeolitemembrane is considerable and treatment temperature is usually from roomtemperature to 150° C., and the treatment may be performed for aboutfrom 10 minutes to 48 hours, and these treatment conditions may beappropriately set according to the nitrate and solvent type to be used.A zeolite membrane after a nitrate treatment may be washed with water,and the nitrogen atom content of the zeolite membrane can be adjusted toa preferred range by repeating washing with water.

(Aluminum Salt Treatment)

In the present invention, a synthesized zeolite membrane may besubjected to an aluminum salt treatment as necessary. An aluminum salttreatment may be performed after an organic template is removed byfiring even in a state including the organic template. An aluminum salttreatment is performed by immersing a zeolite membrane composite in asolution containing, for example, an aluminum salt. As a result, aneffect of an aluminum salt blocking a fine defect present on the filmsurface may be obtained. Further, when an aluminum salt is present inzeolite pores, an aluminum salt treatment has an effect of attractingammonia, and is suitably employed as a technique for improving theammonia permeability. A solvent used for an aluminum salt treatment maybe water or an organic solvent as long as a salt dissolves, and analuminum salt to be used is not limited, and examples thereof includealuminum nitrate, aluminum sulfate, aluminum chloride, aluminumphosphate, aluminum acetate, aluminum carbonate, and aluminum hydroxide.These may be used singly or in combination of two or more kinds thereof.

The concentration of nitrate is usually 10 mol/L or less, and the lowerlimit is 0.1 mol/L or more, preferably 0.5 mol/L or more, and morepreferably 1 mol/L or more. The treatment temperature is usually fromroom temperature to 150° C., and the treatment may be performed forabout from 10 minutes to 48 hours, and these treatment conditions may beappropriately set according to the aluminum salt and solvent type to beused. A zeolite membrane after an aluminum salt treatment may be washedwith water, and the Al atom content of the zeolite membrane can beadjusted by repeating washing with water. In order to increase the Siatom/Al atomic ratio of the present invention, it is preferable toreduce the concentration and treatment amount of an aluminum salt to betreated, or to increase the number of times of water washing after thealuminum salt treatment, and on the other hand, in order to reduce theratio, it is preferable to increase the concentration and treatmentamount of an aluminum salt to be treated, or to reduce the number oftimes of water washing after the aluminum salt treatment.

(Silylation Treatment)

In the present invention, a synthesized zeolite membrane may besubjected to a silylation treatment as necessary. A silylation treatmentis performed by immersing a zeolite membrane composite in a solutioncontaining, for example, an Si compound. As a result, the surface of azeolite membrane can be modified with an Si compound and have specificphysicochemical properties. For example, by reliably forming a layercontaining a large amount of Si—OH on the zeolite membrane surface, thepolarity of the membrane surface can be improved and the separationperformance of a polar molecule can be improved. By modifying thesurface of a zeolite membrane with an Si compound, an effect of blockingfine defects existing on the membrane surface may be obtained.Furthermore, the pore diameter of zeolite can be controlled by asilylation treatment, and a technique for improving the ammoniapermeation selectivity by performing this treatment is also preferablyemployed.

A solvent used for a silylation treatment may be water or an organicsolvent. A solution may be acidic or basic, and in this case, asilylation reaction is catalyzed by the acid or base. A silylating agentto be used is not limited, and alkoxysilane is preferable. The treatmenttemperature is usually from room temperature to 150° C., and thetreatment may be performed for about from 10 minutes to 30 hours, andthese treatment conditions may be appropriately set according to thesilylating agent and solvent type to be used.

In the present invention, the content of nitrogen atoms contained on thesurface of the zeolite membrane of the present invention can becontrolled by a method of adjusting the Al atom/Si atom ratio of zeoliteby selecting a cationic species containing nitrogen atoms in the zeolitecontained in the zeolite membrane, a method of adjusting the content ofnitrogen atoms by adjusting the amount of ion exchange by an ionexchange method, a method of using an organic template(structure-directing agent) containing nitrogen atoms as necessary whenproducing a zeolite membrane, and adjusting the amount of addition andthe heating temperature and heating time when the organic template isremoved by firing, a method of treating a zeolite membrane with nitrate,a method of adjusting the number of times of washing when washing anitric acid-treated zeolite membrane, and appropriately combining thesemethods, as described above.

In the present invention, the content of Al atoms contained on thesurface of the zeolite membrane of the present invention can becontrolled by a method of adjusting the Al atom/Si atom ratio of zeolitecontained in a zeolite membrane, a method of treating a zeolite membranewith an aluminum salt, a method of adjusting the number of times ofwashing when washing an aluminum salt-treated zeolite membrane andappropriately combining these methods, as described above.

In the present invention, the content of alkali metals contained on thesurface of the zeolite membrane of the present invention can becontrolled by a method of adjusting the Al atom/Si atom ratio of zeolitecontained in a zeolite membrane, a method of adjusting the content ofalkali metal elements by adjusting the ion exchange amount by an ionexchange method, a method of adjusting the number of times of washingwhen washing a membrane and appropriately combining these methods, asdescribed above.

A zeolite membrane composite thus produced has excellent characteristicsand can be suitably used as a means for membrane separation of ammoniafrom a mixed gas in the present invention.

EXAMPLES

Hereinafter, although the present invention is described morespecifically based on Examples, the present invention is not limited bythe following Examples without departing from the scope of theinvention. The values of various production conditions and evaluationresults in the following Examples have meanings as preferable values ofthe upper limit or the lower limit in an embodiment of the presentinvention, and a preferred range may be a range defined by a combinationof the above-described upper limit or lower limit value and a value ofthe following Examples or a combination of values of Examples.

In the following, “CHA silicate zeolite” is simply called “CHA zeolite”,“RHO silicate zeolite” is simply called “RHO zeolite”, and “MFI silicatezeolite” is simply called “MFI zeolite”

Example A [Measurement of Separation Performance]

In the following, the separation performance of a zeolite membranecomposite was measured as follows.

(1) Ammonia Separation Test

In an apparatus schematically shown in FIG. 1, an ammonia separationtest was performed as follows. In the apparatus of FIG. 1, a mixed gascontaining ammonia gas (NH₃), nitrogen gas (N₂), and hydrogen (H₂) wassupplied as a supply gas at a flow rate of 100 SCCM between a pressurevessel and a zeolite membrane composite, a back pressure valve wasadjusted in such a manner that the pressure difference between gas onthe supply side and gas permeated through a membrane was constant at 0.3MPa, an exhaust gas discharged from a pipe 10 was analyzed with a microgas chromatograph, and the concentration and flow rate of the permeatedgas were calculated.

In an ammonia separation test, in order to remove components such asmoisture and air from a pressure vessel, after purging with a sample gasto be used for drying and evacuation not less than a measurementtemperature, the sample gas temperature and the differential pressurebetween the supply gas side and the permeated gas side of a zeolitemembrane composite was kept constant and the permeate gas flow rate wasstabilized, then the flow rate of the sample gas (permeated gas)permeated through the zeolite membrane composite was measured and thegas permeance [mol/(m²·s·Pa)] was calculated. As the pressure forcalculating the permeance, a pressure difference (differential pressure)between the supply side and the permeation side of a supply gas wasused. In the case of a mixed gas, a partial pressure difference wasused.

Based on the measurement result, the ideal separation factor α′ wascalculated by the following formula (1).

α′=(Q1/Q2)/(P1/P2)  (1)

[In the formula (1), Q1 and Q2 indicate the permeation amounts[mol·(m²·s)⁻¹] of a highly permeable gas and a low permeable gas,respectively, and P1 and P2 indicate the pressure differences [Pa]between the supply side and the permeation side of the highly permeablegas and the low permeable gas, respectively.]

This coefficient, indicating the ratio between the gas permeances, canbe determined as the ratio obtained by calculating the permeance of eachgas.

Production Example A1: Production of CHA Zeolite Membrane Composite 1

A CHA zeolite membrane composite 1 was produced by the following method.

(Raw Material Mixture for Hydrothermal Synthesis)

First, a raw material mixture for hydrothermal synthesis was prepared asfollows.

To a mixture of 1.45 g of 1 mol/L-NaOH aqueous solution, 5.78 g of 1mol/L-KOH aqueous solution, and 114.6 g of water, 0.19 g of aluminumhydroxide (containing Al₂O₃-53.5% by mass, manufactured by Aldrich Co.,Ltd.) was added and dissolved by stirring to obtain a transparentsolution. To this, 2.43 g of a 25% by mass aqueous solution of TMADAOHwas added as an organic template, and then 10.85 g of colloidal silica(Snowtech-40, manufactured by Nissan Chemical Co., Ltd.) was added andstirred for 2 hours to obtain a raw material mixture for hydrothermalsynthesis. The composition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/KOH/H₂O/TMADAOH=1/0.018/0.02/0.08/100/0.04,SiO₂/Al₂O₃=58.

(Support)

As a porous support, an alumina tube BN1 (outer diameter 6 mm, innerdiameter 4 mm) manufactured by Noritake Company Limited cut into alength of 80 mm, washed with an ultrasonic cleaner, and then dried wasused.

(Seed Crystal Dispersion)

A crystal having a gel composition (molar ratio) ofSiO₂/Al₂O₃/NaOH/KOH/H₂O/TMADAOH=1/0.033/0.1/0.06/20/0.07 obtained byhydrothermal synthesis at 160° C. for 2 days was filtered, washed withwater, and dried to produce CHA zeolite as a seed crystal. The seedcrystal grain size was about from 0.3 to 3 μm. Next, the seed crystalwas dispersed in water in such a manner that the concentration of adispersion was about 1% by mass to produce a seed crystal dispersion(CHA seed crystal dispersion).

(Production of Membrane Composite)

The above-described porous support was prepared, and the support wasimmersed in the seed crystal dispersion for 1 minute, and then dried at100° C. for 1 hour to deposit the seed crystal on the support. The massof the deposited seed crystal was about 0.001 g.

The support with the seed crystal deposited thereon was immersed in thevertical direction in a Teflon (registered trademark) inner cylinder(200 ml) containing the above-described raw material mixture forhydrothermal synthesis, an autoclave was sealed, and heated at 180° C.for 72 hours in a stationary state under a self-generated pressure.After elapse of a predetermined time, after cooling, the support-zeolitemembrane composite was taken out from the raw material mixture forhydrothermal synthesis, washed, and dried at 100° C. for 3 hours.

Next, the dried membrane composite was fired in air in an electricfurnace at 450° C. for 10 hours and at 500° C. for 5 hours, and a CHAzeolite membrane composite 1 from which a template contained in zeolitewas removed was obtained. At this time, the temperature rise rate andthe temperature drop rate from room temperature to 450° C. were both0.5° C./min, and the temperature rise rate and the temperature drop ratefrom 450° C. to 500° C. were both 0.1° C./min. The mass of the CHAzeolite crystallized on the support, which was determined from thedifference between the mass of the membrane composite and the mass ofthe support after firing, was about from 0.279 to 0.289 g. The airpermeation amount of the membrane composite after firing was from 2.4 to2.9 cm³/min.

Example A1 <Evaluation of Membrane Separation Performance>

In a pre-treatment, a mixed gas of 50% by volume H₂/50% by volume N₂ wasintroduced as a supply gas between a pressure vessel and a CHA zeolitemembrane composite 1 described in Production Example A1 at 200° C., thepressure was maintained at about 0.4 MPa, and the inside of a cylinderof the CHA zeolite membrane composite 1 was set at 0.098 MPa(atmospheric pressure) and dried for about 120 minutes.

Using the CHA zeolite membrane composite 1, an ammonia separation testwas performed by the above-described method under the conditions wherethe temperature of the CHA zeolite membrane composite 1 was 100° C.,150° C., 200° C., and 250° C. As the mixed gas, a mixed gas of 12.0% byvolume NH₃/51.0% by volume N₂/37.0% by volume H₂ was used. Table 3 showsthe ammonia concentration in the obtained permeated gas, theammonia/hydrogen (NH₃/H₂) permeance ratio, and the ammonia/nitrogen(NH₃/N₂) permeance ratio. In Table 3, the concentration of ammonia inthe permeated gas is a value obtained by rounding off the first decimalplace.

TABLE 3 100° C. 150° C. 200° C. 250° C. NH₃ concentration in permeatedgas    26%    25%    22%    20% NH₃/N₂ permeance ratio 11 10 8 7 NH₃/H₂permeance ratio 3 3 2 1

Example A2

As a result of evaluating ammonia separation by the same method as inExample A1 except that the CHA zeolite membrane composite 1 described inProduction Example A1 was used, the temperature was set to 100° C., andthe mixed gas was changed to a mixed gas of 3.0% by volume NH₃/24.0% byvolume N₂/73.0% by volume H₂, the ammonia gas concentration in permeatedgas was 4.1% by volume. The obtained results show that ammonia can beseparated from the mixed gas.

Example A3

As a result of evaluating ammonia separation by the same method as inExample A1 except that the CHA zeolite membrane composite 1 described inProduction Example A1 was used, the temperature was set to 100° C., andthe mixed gas was changed to a mixed gas of 2.0% by volume NH₃/19.0% byvolume N₂/79.0% by volume H₂, the ammonia gas concentration in permeatedgas was 2.3% by volume. From the obtained results, it can be seen thatammonia can be separated from the mixed gas.

Comparative Example A1

Ammonia separation was evaluated in the same manner as in Example A1except that the temperature of CHA zeolite membrane composite 1described in Production Example A1 was set to 100° C. and a mixed gas of0.7% by volume NH₃/80.0% by volume N₂/19.3% by volume H₂ was used. As aresult, the ammonia gas concentration in the permeated gas was 0.8% byvolume.

Comparative Example A2

Ammonia separation was evaluated in the same manner as in Example A1except that the temperature of CHA zeolite membrane composite 1described in Production Example A1 was set to 100° C. and a mixed gas of0.8% by volume NH₃/20.1% by volume N₂/79.1% by volume H₂ was used. As aresult, the ammonia gas concentration in the permeated gas was 0.8% byvolume.

As can be seen from Examples A1, A2, A3 and Comparative Examples A1, A2,even in cases in which the same zeolite membrane composite is used, whenthe ammonia gas concentration in the mixed gas is low, it is difficultto separate the ammonia in the mixed gas, whereas when the ammonia gasconcentration in the mixed gas is 1.0% by volume or more, ammonia can beseparated efficiently.

Reference Example A1

As a result of evaluating ammonia separation by the same method as inExample A2 except that the CHA zeolite membrane composite 1 produced inExample A1 was used, the temperature of the CHA zeolite membranecomposite 1 was set to 100° C., and a mixed gas of 12% by volume NH₃/50%by volume N₂/38% by volume H₂ was allowed to pass at a flow rate of 100SCCM, the hydrogen permeance was 7.0×10⁻⁸ [mol/(m²·s·Pa)], the nitrogenpermeance was 2.1×10⁻⁸ [mol/(m²·s·Pa)], and the ammonia permeance was2.4×10⁻⁷ [mol/(m²·s·Pa)]. In contrast, the hydrogen permeance whenhydrogen gas alone was allowed to pass was 1.6×10⁻⁶ [mol/(m²·s·Pa)] andthe nitrogen permeance when nitrogen gas alone was allowed to pass was3.0×10⁻⁷ [mol/(m²·s·Pa)], and from these results, it was found that whenammonia gas was contained in a supply gas, the permeance of hydrogen andnitrogen was considerably reduced. From this result, it is consideredthat when the ammonia gas concentration in the mixed gas is a specificamount or more, the ammonia in the supply gas was adsorbed on thezeolite and exhibited an effect of inhibiting permeation of hydrogen andnitrogen.

Production Example A2: Production of CHA Zeolite Membrane Composite 2

The CHA zeolite membrane composite 1 after removal of the templateobtained in Production Example A1 was placed in a Teflon (registeredtrademark) inner cylinder (65 ml) containing 45 g of 1M ammonium nitrateaqueous solution. An autoclave was sealed and heated at 100° C. for 1hour in a stationary state under a self-generated pressure.

After elapse of a predetermined time, after cooling, the CHA zeolitemembrane was taken out from the aqueous solution, and washing with 100°C. ion exchanged hot water for 1 hour was repeated 3 times, followed bydrying at 100° C. for 4 hours or more to obtain an NH₄ ⁺-type CHAzeolite membrane composite which is a CHA zeolite membrane composite 2.

Example A4 <Evaluation of Membrane Separation Performance>

Ammonia separation evaluation was performed in the same manner as inExample A1 except that the CHA zeolite membrane composite 2 described inProduction Example A2 was used in place of the CHA zeolite membrane 1described in Production Example A1. Table 4 shows the ammoniaconcentration in the obtained permeated gas, the ammonia/hydrogenpermeance ratio, and the ammonia/nitrogen permeance ratio. In Table 4,the concentration of ammonia in the permeated gas is a value obtained byrounding off the first decimal place. From the results in Table 4, itcan be seen that when the ammonia gas concentration in the mixed gas isa specific amount or more, ammonia can be efficiently separated. It canalso be seen that ammonia separation can be performed efficiently evenunder high temperature conditions.

TABLE 4 100° C. 150° C. 200° C. 250° C. NH₃ concentration in permeatedgas    31%    27%    24%    22% NH₃/N₂ permeance ratio 26 16 11 9 NH₃/H₂permeance ratio 6 4 2 2

Production Example A3: Production of RHO Zeolite Membrane Composite 1(Raw Material Mixture for Hydrothermal Synthesis)

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) weredissolved in 125.9 g of water and stirred at 80° C. for 3 hours toobtain a crown ether-alkali aqueous solution. The above-described crownether-alkali aqueous solution was then added dropwise to 8.9 g of Y-type(FAU) zeolite (SAR=30, CBV720 manufactured by Zeolyst International) toprepare a raw material mixture for hydrothermal synthesis. The gelcomposition (molar ratio) of the obtained raw material mixture forhydrothermal synthesis wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.36/0.18/50/0.18.

(Support)

As a porous support, an alumina tube (outer diameter 6 mm, pore diameter0.15 μm, manufactured by Noritake Company Limited) cut into a length of40 mm, washed with water, and then dried was used.

(Seed Crystal Dispersion)

23 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 6 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 5 gof CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolvedin 84 g of water, and the resulting solution was stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution.

Next, the above-described crown ether-alkali aqueous solution was addeddropwise to 30 g of FAU zeolite (SAR=30, CBV720 manufactured by ZeolystInternational), 0.6 g of RHO zeolite synthesized according to WO2015020014 was further added as a seed crystal, and the mixture wasstirred at room temperature for 2 hours to prepare a mixture. Thecomposition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18.

This mixture was aged at room temperature for 24 hours, then placed in apressure vessel and allowed to stand still in an oven at 150° C. for 72hours for hydrothermal synthesis. After this hydrothermal synthesisreaction, the reaction solution was cooled, and a produced crystal wasrecovered by filtration. The recovered crystal was dried at 100° C. for12 hours to obtain a crystal that is RHO zeolite.

The obtained RHO zeolite was pulverized by a ball mill to produce a seedcrystal dispersion. Specifically, 10 g of the above-described RHOzeolite, 300 g of φ3 mm HD Alumina Ball (manufactured by NikkatoCorporation), and 90 g of water were placed in 500 mL polyethylenebottle, and ball-milled for 6 hours to obtain a 10% by mass RHO zeolitedispersion. Water was added to the zeolite dispersion in such a mannerthat the RHO zeolite was 3% by mass to obtain a seed crystal dispersion.

(Production of Membrane Composite)

The seed crystal dispersion was dropped onto the support, and the seedcrystal was deposited on the support by a rubbing method.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis,an autoclave was sealed, and heated at 150° C. for 72 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washing,dried at 100° C. for 5 hours or more. After drying, the air permeationamount in an as-made state was 1.5 L/(m²·min). Next, in order to removea template, the obtained membrane composite was fired at 300 degrees toobtain an RHO zeolite membrane composite. The weight of the RHO zeolitecrystallized on the support determined from the difference between theweight of the zeolite membrane composite and the weight of the supportafter firing was 78 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon (registered trademark) inner cylinder (65 ml)containing 45 g of a 3M ammonium nitrate aqueous solution, and anautoclave was sealed and heated at 110° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO zeolitemembrane was taken out from the aqueous solution, washed with water, andthen dried at 100° C. for 4 hours or more to obtain an NH₄ ⁺-type RHOzeolite membrane composite.

In order to convert the obtained NH₄ ⁺-type RHO zeolite membranecomposite into H⁺-type, this RHO zeolite membrane composite was fired inan electric furnace at 400° C. for 2 hours. At this time, thetemperature rise rate and the temperature drop rate up to 150° C. wereboth set at 2.5° C./min, and the temperature rise rate and thetemperature drop rate from 150° C. to 400° C. were set to 0.5° C./min toobtain an H⁺-type RHO zeolite membrane composite which is an RHO zeolitemembrane composite 1.

Example A5 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 1 described in ProductionExample A3, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed as described above, using theapparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 50% by volume H₂/50% by volume N₂ wasintroduced as a supply gas between a pressure vessel and an RHO zeolitemembrane composite 1 at 250° C., the pressure was maintained at about0.3 MPa, and the inside of a cylinder of the RHO zeolite membranecomposite 1 was set at 0.098 MPa (atmospheric pressure) and dried forabout 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite 1 was0.3 MPa.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 1 to 150° C., 250° C., and 300° C., andthe ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen werecalculated. The results obtained are shown in Table 5. In Table 5, theconcentration of ammonia in the permeated gas is a value obtained byrounding off the first decimal place. The ammonia permeance at 250° C.was 1.0×10⁻⁸ [mol/(m²·s·Pa)]. From the results in Table 5, it can beseen that when the ammonia gas concentration in the mixed gas is aspecific amount or more, ammonia can be efficiently separated. It wasalso confirmed that ammonia could be separated with high selectivitywithout any gaps or defects between zeolite particles under hightemperature conditions.

TABLE 5 150° C. 250° C. 300° C. NH₃ concentration in permeated gas   52%    54%    52% NH₃/N₂ permeance ratio 20 25 24 NH₃/H₂ permeanceratio 5 6 5

Production Example A4: Production of RHO Zeolite Membrane Composite 2

An NH₄ ⁺-type RHO zeolite membrane composite was obtained in the samemanner as in Production Example A3 except that a support with a seedcrystal deposited thereon was immersed in the vertical direction in aTeflon (registered trademark) inner cylinder containing a raw materialmixture for hydrothermal synthesis 2, an autoclave was sealed, andheated at 150° C. for 72 hours under a self-generated pressure, and thatconversion from NH₄ ⁺-type to H⁺-type was not performed.

The NH₄ ⁺-type RHO zeolite membrane composite after removal of thetemplate was then placed into a Teflon (registered trademark) innercylinder (65 ml) containing 45 g of a 1M aluminum nitrate aqueoussolution. An autoclave was sealed and heated at 100° C. for 1 hour in astationary state under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO zeolitemembrane composite was taken out from the aqueous solution, washed withwater, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite, and the obtainedcomposite was again placed in a Teflon (registered trademark) innercylinder (65 ml) containing 45 g of a 1M sodium nitrate aqueoussolution. An autoclave was sealed and heated at 100° C. for 1 hour in astationary state under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO zeolitemembrane was taken out from the aqueous solution, washed with water, andthen dried at 100° C. for 4 hours or more to obtain an RHO zeolitemembrane composite which is the RHO zeolite membrane composite 2,ion-exchanged to Na⁺-type after an Al treatment.

Example A6 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 2 described in ProductionExample A4, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed using the apparatus shown inFIG. 1 in accordance with the above-described method.

In a pre-treatment, a mixed gas of 50% by volume H₂/50% by volume N₂ wasintroduced as a supply gas 7 between a pressure vessel 2 and a zeolitemembrane composite 2 at 250° C., the pressure was maintained at about0.3 MPa, and the inside of a cylinder of the RHO zeolite membranecomposite 2 was set at 0.098 MPa (atmospheric pressure) and dried forabout 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas 7side and the permeated gas 8 side of the zeolite membrane composite 2was 0.3 MPa.

The mixed gas was then allowed to pass while changing the temperature ofthe RHO zeolite membrane composite 2 to 100° C. and 250° C., and theammonia concentration in the obtained permeated gas and the permeanceratio of ammonia/hydrogen and ammonia/nitrogen were calculated. Theresults obtained are shown in Table 6. In Table 6, the concentration ofammonia in the permeated gas is a value obtained by rounding off thefirst decimal place. From the results in Table 6, it can be seen thatwhen the ammonia gas concentration in the mixed gas is a specific amountor more, ammonia can be efficiently separated. It was also confirmedthat the RHO zeolite membrane composite was able to separate ammoniawith high selectivity under high temperature conditions. The ammoniapermeance at 250° C. was 2.0×10⁻⁸ [mol/(m²·s·Pa)].

TABLE 6 100° C. 250° C. NH₃ concentration in permeated gas    60%    56%NH₃/N₂ permeance ratio 29 31 NH₃/H₂ permeance ratio 7 6

Production Example A5: Production of RHO Zeolite Membrane Composite 3, 4

A seed crystal and a support were prepared in the same manner as inProduction Example A4 except that water was added in such a manner thatRHO zeolite was 1% by mass to obtain a seed crystal dispersion, and asupport whose inside was evacuated was immersed in this seed crystaldispersion for 1 minute, and then the seed crystal was deposited on thesupport by a rubbing method with the inside of the support evacuated.

Next, the support on which the seed crystal was deposited was immersedin a Teflon (registered trademark) inner cylinder containing a rawmaterial mixture for hydrothermal synthesis produced by the same methodas in Production Example A4 in the vertical direction to seal anautoclave, and heated at 160° C. for 24 hours under a self-generatedpressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washing,dried at 100° C. for 5 hours or more. After drying, the air permeationamount in an as-made state was 0.0 L/(m²·min). Next, in order to removea template, the obtained membrane composite was fired to obtain an RHOzeolite membrane composite. The weight of the RHO zeolite crystallizedon the support determined from the difference between the weight of thezeolite membrane composite and the weight of the support after firingwas 62 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M ammonium nitrate aqueous solution. An autoclavewas sealed and heated at 100° C. for 1 hour in a stationary state undera self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Treatment with 1M ammonium nitrate aqueous solution was then repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite as an RHO zeolite membranecomposite 3.

The NH₄ ⁺-type RHO zeolite membrane composite 3 obtained was placed intoa Teflon (registered trademark) inner cylinder (65 ml) containing 45 gof a 1M aluminum nitrate aqueous solution, and an autoclave was sealedand heated at 100° C. for 1 hour in a stationary state under aself-generated pressure.

After elapse of a predetermined time, after cooling, the RHO zeolitemembrane composite 3 was taken out from the aqueous solution, washedwith water, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite which is an RHOzeolite membrane composite 4.

Example A7 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 4 described in ProductionExample A5, an ammonia separation test from a mixed gas of ammonia(NH₃)/hydrogen (H₂)/nitrogen (N₂) was conducted using the apparatusshown in FIG. 1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and the RHO zeolite membrane composite 4 at 250° C., the pressurewas maintained at about 0.3 MPa, and the inside of a cylinder of the RHOzeolite membrane composite 4 was set at 0.098 MPa (atmospheric pressure)and dried for about 120 minutes. A mixed gas of 12% by volume NH₃/51% byvolume N₂/37% by volume H₂ was then allowed to pass at 100 SCCM, and theback pressure was set to 0.4 MPa. At this time, the differentialpressure between the supply gas side and the permeated gas side of theRHO zeolite membrane composite 4 was 0.3 MPa. 3.9 SCCM of argon wassupplied from the supply gas 9 as a sweep gas.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 4 to 250° C., 300° C., and 325° C., andthe ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 7. In Table 7, the concentration of ammonia in the permeated gasis a value obtained by rounding off the first decimal place. From theseresults, it was confirmed that NH₄ ⁺-type RHO zeolite membrane treatedwith Al under high temperature conditions was able to separate ammoniawith high selectivity. The ammonia permeance at 250° C. was 1.0×10⁻⁸[mol/(m²·s·Pa)], and the ammonia permeance at 325° C. was 2.0×10⁻⁸[mol/(m²·s·Pa)]. From the results in Table 7, it can be seen that whenthe ammonia gas concentration in the mixed gas is a specific amount ormore, ammonia can be efficiently separated. It can also be seen thatammonia separation can be performed efficiently even under hightemperature conditions.

TABLE 7 250° C. 300° C. 325° C. NH₃ concentration in permeated gas   71%    70%    71% NH₃/N₂ permeance ratio 43 59 63 NH₃/H₂ permeanceratio 15 13 13

Production Example A6: Production of RHO Zeolite Membrane Composite 5

An NH₄ ⁺-type RHO zeolite membrane composite obtained by the same methodas the RHO zeolite membrane composite 3 of Production Example A5 wasplaced into a Teflon (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M sodium nitrate aqueous solution. An autoclavewas sealed and heated at 100° C. for 1 hour in a stationary state undera self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour, followed by drying at 100° C. for 4hours or more to obtain an RHO zeolite membrane composite ion-exchangedto Na⁺-type. Next, the Na⁺-type RHO zeolite membrane obtained was placedinto a Teflon (registered trademark) inner cylinder (65 ml) containing50 g of a 1M aluminum nitrate aqueous solution, and an autoclave wassealed and heated at 100° C. for 1 hour in a stationary state under aself-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution, and 1 hour washing with 100° C.ion exchanged hot water was repeated 3 times, followed by drying at 100°C. for 4 hours or more to obtain an Al-treated Na⁺-type RHO zeolitemembrane composite which is an RHO zeolite membrane composite 5.

Example A8 <Evaluation of Membrane Separation Performance>

A separation test of a mixed gas of 12.0% by volume NH₃/51.0% by volumeN₂/37.0% by volume H₂ was conducted in the same manner as in Example A7except that the RHO zeolite membrane composite 5 described in ProductionExample A6 was used in place of the RHO zeolite membrane composite 4described in Production Example A5, and that argon was supplied in anamount of 8.3 SCCM as a sweep gas.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 8. In Table 8, the concentration of ammonia in the permeated gasis a value obtained by rounding off the first decimal place. The ammoniapermeance at 250° C. was 4.4×10⁻⁸ [mol/(m²·s·Pa)], and the ammoniapermeance at 325° C. was 1.1×10⁻⁷ [mol/(m²·s·Pa)]. From these results,it can be seen that when the ammonia gas concentration in the mixed gasis a specific amount or more, ammonia can be efficiently separated. Itwas also confirmed that ammonia could be separated with high selectivityeven under high temperature conditions.

TABLE 8 250° C. 300° C. 325° C. NH₃ concentration in permeated gas    82%     77%     66% NH₃/N₂ permeance ratio 259 237 230 NH₃/H₂permeance ratio 44 35 34

Example A9

As a result of evaluating ammonia separation by the same method as inThe obtained results show that ammonia can be separated from

Example A10

As a result of evaluating ammonia separation by the same method as inExample A8 except that the RHO zeolite membrane composite 5 described inProduction Example A6 was used, the temperature was set to 250° C., andthe mixed gas was changed to a mixed gas of 3.0% by volume NH₃/20.0% byvolume N₂/77.0% by volume H₂, the ammonia gas concentration in permeatedgas was 27.6% by volume. From the obtained results, it can be seen thatammonia can be separated from the mixed gas.

Production Example A7: Production of RHO Zeolite Membrane Composite 6(Mixture for Hydrothermal Synthesis)

The following raw material mixture for hydrothermal synthesis wasprepared.

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H2O (manufactured by Mitsuwa Chemical Co., Ltd.) 6.8 g of18-crown-6-ether (manufactured by Tokyo Chemical Industry Co., Ltd.),2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 4.2 g ofCsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolved in125.9 g of water and stirred at 80° C. for 3 hours to obtain a crownether-alkali aqueous solution. The above-described crown ether-alkaliaqueous solution was then added dropwise to 8.9 g of Y-type (FAU)zeolite (SAR=30, CBV720 manufactured by Zeolyst International) and 0.2 gof aluminum hydroxide (Al₂O₃, 53.5% by mass, manufactured by AldrichCo., Ltd.) to prepare a raw material mixture for hydrothermal synthesis.The gel composition (molar ratio) of the obtained raw material mixturefor hydrothermal synthesis wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.040/0.36/0.18/50/0.18.

(Production of Membrane Composite)

A seed crystal and a support were prepared in the same manner as inProduction Example A4 except that water was added in such a manner thatRHO zeolite was 1% by mass to obtain a seed crystal dispersion, and asupport whose inside was evacuated was immersed in this seed crystaldispersion for 1 minute, and then the seed crystal was deposited on thesupport by a rubbing method with the inside of the support evacuated.

Next, the support on which the seed crystal was deposited was immersedin a Teflon (registered trademark) inner cylinder containing a rawmaterial mixture for hydrothermal synthesis in the vertical direction toseal an autoclave, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washing,dried at 100° C. for 5 hours or more. After drying, the air permeationamount in an as-made state was 0.0 L/(m²·min). Next, in order to removea template, the obtained membrane composite was fired to obtain an RHOzeolite membrane composite. The weight of the RHO zeolite crystallizedon the support determined from the difference between the weight of thezeolite membrane composite and the weight of the support after firingwas 56 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M ammonium nitrate aqueous solution. An autoclavewas sealed and heated at 100° C. for 1 hour in a stationary state undera self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Next, treatment with 1M ammonium nitrate aqueous solution was thenrepeated 5 times, followed by drying at 100° C. for 4 hours or more toobtain an NH₄ ⁺-type RHO zeolite membrane composite.

The NH₄ ⁺-type RHO zeolite membrane composite was placed into a Teflon(registered trademark) inner cylinder (65 ml) containing 50 g of a 1Maluminum nitrate aqueous solution. An autoclave was sealed and heated at100° C. for 1 hour in a stationary state under a self-generatedpressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution, washed with water, and thendried at 100° C. for 4 hours or more to obtain an Al-treated NH₄ ⁺-typeRHO zeolite membrane composite which is an RHO zeolite membranecomposite 6.

Example A11 <Evaluation of Membrane Separation Performance>

A separation test of a mixed gas of 12% by volume NH₃/51% by volumeN₂/37% by volume H₂ was conducted under the conditions where thetemperature of the RHO zeolite membrane composite 6 was 250° C. and 325°C. in the same manner as in Example A7 except that the RHO zeolitemembrane composite 6 described in Production Example A7 was used inplace of the RHO zeolite membrane composite 4 described in ProductionExample A5.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 9. In Table 9, the concentration of ammonia in the permeated gasis a value obtained by rounding off the first decimal place. From theseresults, it can be seen that when the ammonia gas concentration in themixed gas is a specific amount or more, ammonia can be efficientlyseparated. It was also confirmed that an RHO membrane produced using agel composition with an increased Al content could separate ammonia withhigher selectivity even under high temperature conditions. The ammoniapermeance at 250° C. was 1.3×10⁻⁸ [mol/(m²·s·Pa)], and the ammoniapermeance at 325° C. was 2.8×10⁻⁸ [mol/(m²·s·Pa)].

250° C. 325° C. NH₃ concentration in permeated gas     85%     81%NH₃/N₂ permeance ratio 408 368 NH₃/H₂ permeance ratio 132 69

Production Example A8: Production of MFI Zeolite Membrane Composite 1(Raw Material Mixture for Hydrothermal Synthesis)

A raw material mixture for hydrothermal synthesis was prepared by thefollowing method.

To a mixture of 13.65 g of a 50% by weight NaOH aqueous solution and 101g of water, 0.15 g of sodium aluminate (containing Al₂O₃-62.2% by mass)was added and stirred at room temperature for 10 minutes. To this, 32.3g of colloidal silica (Snowtech-40, manufactured by Nissan Chemical Co.,Ltd.) was added and stirred for 5 hours at 50 degrees to obtain a rawmaterial mixture for hydrothermal reaction. The composition (molarratio) of this raw material mixture for hydrothermal reaction wasSiO₂/Al₂O₃/NaOH/H₂O=3.05/0.013/0.193/100, SiO₂/Al₂O₃=239.

(Seed Crystal Dispersion)

ZSM5 zeolite (manufactured by Tosoh Corporation, HSZ-800 series 822H0A)was ground in a mortar, and the seed crystal was dispersed in such amanner that the concentration thereof was about 0.4% by mass to preparea seed crystal dispersion.

(Production of Membrane Composite)

After immersing a porous support subjected to the same treatment as inProduction Example A1 in the above-described seed crystal dispersion for1 minute, the support was dried at 70° C. for 1 hour, again immersed ina seed crystal dispersion for 1 minute, and then dried at 70° C. for 1hour to deposit the seed crystal on the support. The mass of thedeposited seed crystal was about 0.0016 g. A porous support having aseed crystal deposited thereon was prepared by the above-describedmethod.

Three supports with the seed crystal deposited thereon were eachimmersed in the vertical direction in the above-described Teflon(registered trademark) inner cylinder (200 ml) containing theabove-described raw material mixture for hydrothermal synthesis, anautoclave was sealed, and heated at 180° C. for 30 hours in a stationarystate under a self-generated pressure. After elapse of a predeterminedtime, after cooling, the support-zeolite membrane composite was takenout from the reaction mixture, washed, and dried at 100° C. for 3 hoursto obtain an MFI zeolite membrane composite 1. The mass of MFI zeolitecrystallized on the support was from 0.26 to 0.28 g. The air permeationamount of the membrane composite after firing was from 0.0 to 0.1cm³/min.

Example A12 <Evaluation of Membrane Separation Performance>

Ammonia separation evaluation was performed in the same manner as inExample A1 except that the MFI zeolite membrane composite 1 described inProduction Example A8 was used in place of the CHA zeolite membranecomposite 1 described in Production Example A1. Table 10 shows theammonia concentration in the obtained permeated gas, theammonia/hydrogen permeance ratio, and the ammonia/nitrogen permeanceratio. In Table 10, the concentration of ammonia in the permeated gas isa value obtained by rounding off the first decimal place. The permeanceof ammonia at 250° C. was 7.5×10⁻⁸ [mol/(m²·s·Pa)]. From these results,it can be seen that when the ammonia gas concentration in the mixed gasis a specific amount or more, ammonia can be efficiently separated. Itwas also confirmed that even when the temperature was changed from 150°C. to 250° C., ammonia permeated through the membrane with highselectivity. It was therefore confirmed that ammonia could be separatedwith high selectivity even under high temperature conditions.

TABLE 10 100° C. 150° C. 200° C. 250° C. NH₃ concentration in permeatedgas    46%    44%    46%    45% NH₃/N₂ permeance ratio 18 18 23 23NH₃/H₂ permeance ratio 5 4 5 5

Example A13

As a result of evaluating ammonia separation by the same method as inExample A12 except that the temperature was set to 250° C., and themixed gas was changed to a mixed gas of 2.0% by volume NH₃/20.0% byvolume N₂/78.0% by volume H₂, the ammonia gas concentration in permeatedgas was 7.0% by volume. The obtained results show that ammonia can beseparated from the mixed gas.

Example A14

As a result of evaluating ammonia separation by the same method as inExample A12 except that the temperature was set to 250° C., and themixed gas was changed to a mixed gas of 3.0% by volume NH₃/20.0% byvolume N₂/77.0% by volume H₂, the ammonia gas concentration in permeatedgas was 10.7% by volume. The obtained results show that ammonia can beseparated from the mixed gas.

Reference Example A2

As a result of evaluating ammonia separation by the same method as inExample A12 except that the MFI zeolite membrane composite 1 produced inProduction Example A8 was used, the temperature of the MFI zeolitemembrane composite 1 was set to 250° C., and a mixed gas of 12% byvolume NH₃/50% by volume N₂/38% by volume H₂ was allowed to pass at aflow rate of 100 SCCM, the hydrogen permeance was 1.6×10⁻⁸[mol/(m²·s·Pa)], the nitrogen permeance was 3.3×10⁻⁹ [mol/(m²·s·Pa)],and the ammonia permeance was 7.5×10⁻⁸ [mol/(m²·s·Pa)]. In contrast, thehydrogen permeance when hydrogen gas alone was allowed to pass was4.7×10⁻⁷ [mol/(m²·s·Pa)] and the nitrogen permeance when nitrogen gasalone was allowed to pass was 3.0×10⁻⁷ [mol/(m²·s·Pa)], and from theseresults, it was found that when ammonia gas was contained in a supplygas, the permeance of hydrogen and nitrogen was considerably reduced.From this result, it is considered that when the ammonia gasconcentration in the mixed gas is a specific amount or more, the ammoniain the supply gas was adsorbed on the zeolite and exhibited an effect ofinhibiting permeation of hydrogen and nitrogen.

Table 11 shows data of Examples A1 to A3, A8 to 10, A12 to 14, andComparative Examples A1 to A2. The evaluation results at 100° C. forExamples A1 to A3 and Comparative Examples A1 and A2 and at 250° C. forExamples A8 to 10 and A12 to 14 are shown. From these results, it wasfound that the concentration degree of ammonia with respect to hydrogenand nitrogen increases when the concentration of ammonia gas in a mixedgas is not less than a specific amount.

TABLE 11 Membrane NH₃ Raw material permeated gas Concentration degreeconcentration gas concentration concentration (membrane permeateddegree/H₂ Membrane (vol %) (vol %) gas/raw material gas) concentrationtype H₂ N₂ NH₃ H₂ N₂ NH₃ H₂ N₂ NH₃ degree Example A1 CHA 37.0 51.0 12.051.8 28.0 26.4 1.40 0.55 2.20 1.6 Example A2 CHA 73.0 24.0 3.0 80.1 15.84.1 1.10 0.66 1.36 1.2 Example A3 CHA 79.0 19.0 2.0 83.4 14.3 2.3 1.060.75 1.16 1.1 Example A8 RHO 37.0 51.0 12.0 14.5 3.3 82.2 0.39 0.06 6.8517.5 Example A9 RHO 78.0 20.0 2.0 76.7 3.4 19.9 0.98 0.17 9.97 10.1Example A10 RHO 77.0 20.0 3.0 69.3 3.0 27.6 0.90 0.15 9.21 10.2 ExampleA12 MR 37.0 51.0 12.0 42.6 12.6 44.8 1.15 0.25 3.73 3.2 Example A13 MFI78.0 20.0 2.0 73.3 19.7 7.0 0.94 0.98 3.52 3.7 Example A14 MEI 77.0 20.03.0 70.8 18.5 10.7 0.92 0.92 3.56 3.9 Comparative CHA 19.3 80.0 0.7 23.474.3 0.8 1.21 0.93 1.14 0.9 Example A1 Comparative CHA 79.1 20.1 0.882.1 17.1 0.8 1.04 0.85 1.05 1.0 Example A2

Example B [Measurement of Physical Properties and SeparationPerformance]

In the following, the physical properties and separation performance ofzeolite or a zeolite membrane composite were measured as follows.

(1) X-Ray Diffraction (XRD) Measurement

XRD measurement was carried out based on the following conditions.

-   Apparatus name: New D8 ADVANCE manufactured by Bruker Corporation-   Optical system: Bragg-Brentano optical system-   Optical system specifications Incident side: Enclosed X-ray tube    (CuKα)    -   Soller Slit (2.5°)    -   Divergence Slit (Variable Slit)    -   Sample stage: XYZ stage    -   Light-receiving side: Semiconductor array detector (Lynx Eye 1D        mode)        -   Ni-filter            -   Soller Slit (2.5°)    -   Goniometer radius: 280 mm-   Measurement conditions X-ray output (CuKα): 40 kV, 40 mA    -   Scanning axis: θ/2θ    -   Scanning range (2θ): 5.0-70.0°    -   Measurement mode: Continuous    -   Read width: 0.010    -   Counting time: 57.0 sec (0.3 sec×190ch)    -   Automatic variable slit (Automatic-DS): 1 mm (irradiation width)

The measurement data was subjected to variable->fixed slit correction.

X-rays were irradiated in a direction perpendicular to the axialdirection of a cylindrical tube. In order to avoid noise or the like asmuch as possible, X-rays were set to be mainly irradiated along not aline in contact with the surface of a sample stage, but the other lineabove the surface of the sample stage, of two lines where a cylindricaltubular membrane composite on the sample stage and planes parallel tothe surface of the sample stage were in contact with.

The irradiation width was measured with an automatic variable slit fixedat 1 mm, and variable slit->fixed slit conversion was performed usingXRD analysis software JADE+9.4 (English version), created by MaterialsData, Inc. to obtain an XRD pattern.

(2) XPS Measurement (Na, Si, Al, N)

-   -   XPS measurement was carried out based on the following        conditions.    -   Model name: Quantum 2000 manufactured by ULVAC-PHI, Incorporated    -   X-ray source for measurement: Monochromatic Al-Kα, output 16        kV-34 W        -   (X-ray generation area 170 ump)    -   Charge neutralization: electron gun 5 μA, ion gun 3V    -   Spectroscopic system: Path energy    -   Wide spectrum: 187.70 eV    -   Narrow spectrum (N1s, O1s, Na1s, Al2p, Si2p, Cs3d5)): 58.70 eV        -   When Cs was detected, the peak position of Cs3d5 and Al₂p            overlapped, and therefore, the peak of Al2s was used instead            of Al2p. (It was confirmed that there was no difference in            the analytical value of the surface composition using either            Al2p or Al2s using a sample containing no Cs.)    -   Measurement area: 300 μm square    -   Extraction angle: 45° (from surface)    -   Energy correction; Si2p=103.4 eV

Quantification was performed using a sensitivity correction coefficientprovided by ULVAC-PHI, Incorporated, and the background for quantitativecalculation was determined by the Shirley method.

(3) Air Permeation Amount

One end of the zeolite membrane composite was sealed, the other end wasconnected to 5 kPa vacuum line in a sealed state, and the air flow ratewas measured with a mass flow meter installed between the vacuum lineand the zeolite membrane composite, to obtain an air permeation amount[L/(m²·h)]. 8300 made by KOFLOC, Corp., for N₂ gas, maximum flow rate500 ml/min (in terms of 20° C., 1 atm) was used as the mass flow meter.When the display of the mass flow meter was 10 ml/min (in terms of 20°C., 1 atm) or less in 8300 manufactured by KOFLOC, Corp., measurementwas carried out using MM-2100M manufactured by Lintec Corporation, forAir gas, and a maximum flow rate of 20 ml/min (in terms of 0° C., 1atm).

In FIG. 1, a cylindrical zeolite membrane composite 1 is installed in athermostat (not shown) in a state of being stored in a pressure vessel 2made of stainless steel. The thermostat is provided with a temperaturecontrol device in such a manner that the temperature of a supply gas canbe adjusted.

One end of the cylindrical zeolite membrane composite 1 is sealed withan end pin 3 having a T-shaped cross section. The other end of thezeolite membrane composite 1 is connected to a discharge pipe 10 forpermeated gas 8 through a connection portion 4, and a pipe 10 extends tothe outside of the pressure vessel 2. Further, a pressure gauge 5 formeasuring the supply pressure of a supply gas 7 from a supply pipe 12and a back pressure valve 6 for adjusting the supply pressure areconnected to a gas discharge pipe 13 from the pressure vessel 2. Eachconnection portion is connected with favorable airtightness.

In the apparatus of FIG. 1, when performing a single component gaspermeation test, the supply gas (sample gas) 7 was supplied between thepressure vessel 2 and the zeolite membrane composite 1 at a constantflow rate, the pressure on the supply side was made constant by the backpressure valve 6, and the permeated gas 8 that had passed through thezeolite membrane composite 1 was measured with a flow meter connected tothe pipe 10.

One end of the cylindrical zeolite membrane composite 1 is sealed withan end pin 3 having a T-shaped cross section. The other end of thezeolite membrane composite 1 is connected to a discharge pipe 11 forpermeated gas 8 through a connection portion 4, and a pipe 11 extends tothe outside of the pressure vessel 2. A pressure gauge 5 for measuringthe pressure on the supply side of the supply gas 7 is connected to asupply pipe 12 for the supply gas (sample gas) 7 to the pressure vessel2. Each connection portion is connected with favorable airtightness.

(4) Ammonia Separation Test

In the apparatus schematically shown in FIG. 1, an ammonia separationtest was performed as follows. In the apparatus of FIG. 1, a mixed gascontaining ammonia, nitrogen, and hydrogen as a supply gas was suppliedbetween the pressure vessel and the zeolite membrane composite at a flowrate of 100 SCCM, the back pressure valve was adjusted in such a mannerthat the pressure difference between gas on the supply side and gas thathad passed through the membrane was constant at 0.3 MPa, helium whoseflow rate was controlled by a mass flow controller was mixed withexhaust gas discharged from the pipe 10 as a standard substance,analysis was performed with a micro gas chromatograph, and theconcentration and flow rate of permeated gas were calculated.

In the ammonia separation test, in order to remove components such asmoisture and air from the pressure vessel, for drying and exhausting ator higher than a measurement temperature, after purging with a samplegas to be used, the sample gas temperature and the pressure differencebetween the supply gas side and the permeated gas side of a zeolitemembrane composite were made constant, and after the permeate gas flowrate was stabilized, the flow rate of the sample gas (permeated gas)permeated through the zeolite membrane composite was measured, and thegas permeance [mol/(m²·s·Pa)] was calculated. As the pressure forcalculating the permeance, the pressure difference (differentialpressure) between the supply side and the permeation side of a supplygas was used. In the case of a mixed gas, a partial pressure differencewas used.

Based on the measurement result, the ideal separation factor α′ wascalculated by the following formula (1).

α′=(Q1/Q2)/(P1/P2)  (1)

[In the formula (1), Q1 and Q2 indicate the permeation amounts[mol·(m²·s)⁻¹] of a highly permeable gas and a low permeable gas,respectively, and P1 and P2 indicate the pressure differences [Pa]between the supply side and the permeation side of the highly permeablegas and the low permeable gas, respectively.]

This coefficient, indicating the ratio between the gas permeances, canbe determined as the ratio obtained by calculating the permeance of eachgas.

Production Example B1: Production of RHO Zeolite Membrane Composite 1, 2

RHO zeolite membrane composites 1 and 2 were produced by the followingmethod. Prior to the production of the RHO zeolite membrane composites 1and 2, a raw material mixture for hydrothermal synthesis 1, a support,and a seed crystal dispersion 1 were prepared as follows.

(Raw Material Mixture for Hydrothermal Synthesis 1)

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) weredissolved in 125.9 g of water and stirred at 80° C. for 3 hours toobtain a crown ether-alkali aqueous solution. The above-described crownether-alkali aqueous solution was added dropwise to 8.9 g of Y (FAU)zeolite (SAR=30, CBV720, manufactured by Zeolyst International) toprepare a raw material mixture for hydrothermal synthesis. The gelcomposition (molar ratio) of the obtained raw material mixture forhydrothermal synthesis 1 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.36/0.18/50/0.18.

(Support)

As a porous support, an alumina tube (outer diameter 6 mm, innerdiameter 4 mm, pore diameter 0.15 μm, manufactured by Noritake CompanyLimited) cut into a length of 80 mm, washed with water, and then driedwas used.

(Seed Crystal Dispersion 1)

23 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 6 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 5 gof CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolvedin 84 g of water, and the resulting solution was stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution.

Next, the above-described crown ether-alkali aqueous solution was addeddropwise to 30 g of FAU zeolite (SAR=30, CBV720 manufactured by ZeolystInternational), 0.6 g of RHO zeolite synthesized according to WO2015020014 was further added as a seed crystal, and the mixture wasstirred at room temperature for 2 hours to prepare a mixture. Thecomposition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18.

The mixture was aged at room temperature for 24 hours, then placed in apressure vessel and allowed to stand still in an oven at 150° C. for 72hours for hydrothermal synthesis. After this hydrothermal synthesisreaction, the reaction solution was cooled, and a produced crystal wasrecovered by filtration. The recovered crystal was dried at 100° C. for12 hours to obtain a crystal that is RHO zeolite.

The obtained RHO zeolite was pulverized by a ball mill to produce a seedcrystal dispersion. Specifically, 10 g of the above-described RHOzeolite, 300 g of p 3 mm HD Alumina Ball (manufactured by NikkatoCorporation), and 90 g of water were placed in 500 mL polyethylenebottle, and ball-milled for 6 hours to obtain a 10% by mass RHO zeolitedispersion. Water was added to the zeolite dispersion in such a mannerthat the RHO zeolite was 1% by mass to obtain a seed crystal dispersion1.

(Production of Zeolite Membrane Composite)

Next, a support whose inside was evacuated was immersed in this seedcrystal dispersion 1 for 1 minute, and then the seed crystal wasdeposited on the support by a rubbing method with the inside of thesupport evacuated.

The support with the seed crystal deposited thereon was immersed in thevertical direction in a Teflon (registered trademark) inner cylindercontaining the raw material mixture for hydrothermal synthesis, anautoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0L/(m²·min). Next, in order to remove a template, the obtained membranecomposite was fired to obtain an RHO zeolite membrane composite. The RHOzeolite membrane composite was heated from room temperature to 100° C.in 2 hours, and from 100° C. to 300° C. in 20 hours, and after firing at300° C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 62 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Treatment with 1M ammonium nitrate aqueous solution was then repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite as an RHO zeolite membranecomposite 1.

The NH₄ ⁺-type RHO zeolite membrane composite 1 obtained was placed intoa Teflon container (registered trademark) inner cylinder (65 ml)containing 45 g of a 1M aluminum nitrate aqueous solution, and anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the NH₄ ⁺-type RHOzeolite membrane composite 1 subjected to the above-described treatmentwas taken out from the aqueous solution, washed with ion exchangedwater, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite which is an RHOzeolite membrane composite 2. As a result of measuring the zeolitemembrane of the zeolite membrane composite by XPS, the nitrogen atom/Alatom molar ratio of the zeolite membrane was 0.42, and the Si atom/Alatom molar ratio was 3.01.

Example B1 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 2 described in ProductionExample B1, an ammonia separation test from a mixed gas of ammonia gas(NH₃)/hydrogen gas (H₂)/nitrogen gas (N₂) was specifically conducted inaccordance with the following method using the apparatus shown in FIG.1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and the RHO zeolite membrane composite 2 at 250° C., the pressurewas maintained at about 0.3 MPa, and the inside of a cylinder of the RHOzeolite membrane composite 2 was set at 0.098 MPa (atmospheric pressure)and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass as a supply gas at 100 SCCM, and the back pressurewas set to 0.4 MPa. At this time, the differential pressure between thesupply gas side and the permeated gas side of the RHO zeolite membranecomposite 2 was 0.3 MPa. 3.9 SCCM of argon was supplied from the supplygas 9 as a sweep gas.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 2 to 250° C., 300° C., and 325° C., andthe ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 12. From the results of Table 12, it can be seen that ammonia canbe efficiently separated by using an NH₄ ⁺-type RHO zeolite membranehaving a nitrogen atom/Al atom molar ratio of 0.42 in XPS measurement.It was confirmed that the NH₄ ⁺-type RHO zeolite membrane having anitrogen atom/Al atom molar ratio of 0.42 in XPS measurement canseparate ammonia with high selectivity under a high temperaturecondition. The ammonia permeance at 250° C. was 1.0×10⁻⁸[mol/(m²·s·Pa)], and the ammonia permeance at 325° C. was 2.0×10⁻⁸[mol/(m²·s·Pa)].

TABLE 12 250° C. 300° C. 325° C. NH₃ concentration in permeated gas   71%    70%    71% NH₃/N₂ permeance ratio 43 59 63 NH₃/H₂ permeanceratio 15 13 13

Production Example B2: Production of RHO Zeolite Membrane Composite 3

An RHO zeolite membrane composite 3 was produced by the followingmethod. The support used was the same support as in Production ExampleB1, and the seed crystal dispersion used was the same as the seedcrystal dispersion 1 in Production Example B1.

(Mixture for Hydrothermal Synthesis 2)

The following raw material mixture for hydrothermal synthesis 2 wasprepared. 6.8 g of 18-crown-6-ether (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 2.1 g of NaOH (manufactured by Kishida ChemicalCo., Ltd.), and 4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co.,Ltd.) were dissolved in 125.9 g of water and stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution. Theabove-described crown ether-alkali aqueous solution was then addeddropwise to 8.9 g of Y-type (FAU) zeolite (SAR=30, CBV720 manufacturedby Zeolyst International) and 0.2 g of aluminum hydroxide (Al₂O₃, 53.5%by mass, manufactured by Aldrich Co., Ltd.) to prepare a raw materialmixture for hydrothermal synthesis. The gel composition (molar ratio) ofthe obtained raw material mixture for hydrothermal synthesis 2 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.040/0.36/0.18/50/0.18.

(Production of Membrane Composite)

A support whose inside was evacuated was immersed in this seed crystaldispersion 1 for 1 minute, and then the seed crystal was deposited onthe support by a rubbing method with the inside of the supportevacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis2, an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0L/(m²·min). Next, in order to remove a template, the obtained membranecomposite was fired to obtain an RHO zeolite membrane composite. The RHOzeolite membrane composite was heated from room temperature to 100° C.in 2 hours, and from 100° C. to 300° C. in 20 hours, and after firing at300° C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 56 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Next, treatment with 1M ammonium nitrate aqueous solution was repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite.

The NH₄ ⁺-type RHO zeolite membrane composite 1 was placed into a Tefloncontainer (registered trademark) inner cylinder (65 ml) containing 50 gof a 1M aluminum nitrate aqueous solution. An autoclave was sealed andheated at 100° C. for 1 hour in a stationary state under aself-generated pressure.

After elapse of a predetermined time, after cooling, the NH₄ ⁺-type RHOzeolite membrane composite subjected to the above-described treatmentwas taken out from the aqueous solution, washed with ion exchangedwater, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite which was the RHOzeolite membrane composite 3. The nitrogen atom/Al atom molar ratio ofthe zeolite membrane measured by XPS was 0.76, and the Si atom/Al atommolar ratio was 6.65.

Example B2 <Evaluation of Membrane Separation Performance>

A separation test of a mixed gas of 12% by volume NH₃/51% by volumeN₂/37% by volume H₂ was conducted under the conditions of 250° C. and325° C. in the same manner as in Example B1 except that the RHO zeolitemembrane composite 3 described in Production Example B2 was used inplace of the RHO zeolite membrane composite 2 described in ProductionExample B1, and that the supply amount of argon which was a sweep gaswas changed to 8.3 SCCM.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 13. From the results of Table 13, it can be seen that by usingthis NH₄ ⁺-type RHO zeolite membrane having a nitrogen atom/Al atommolar ratio of 0.76 as measured by XPS, ammonia can be separatedefficiently. It was also confirmed that an RHO membrane produced using agel composition with an increased Al atom content could separate ammoniawith higher selectivity even under high temperature conditions. Theammonia permeance at 250° C. was 1.3×10⁻⁸ [mol/(m²·s·Pa)], and theammonia permeance at 325° C. was 2.8×10⁻⁸ [mol/(m²·s·Pa)].

TABLE 13 250° C. 325° C. NH₃ concentration in permeated gas     85%    81% NH₃/N₂ permeance ratio 408 368 NH₃/H₂ permeance ratio 132 69

Production Example B3: Production of RHO Zeolite Membrane Composite 4

An RHO zeolite membrane composite 4 was produced by the followingmethod. A raw material mixture for hydrothermal synthesis and a supportwere the same as the raw material mixture for hydrothermal synthesis 1and the support of Production Example B1, respectively.

(Seed Crystal Dispersion 2)

A seed crystal dispersion 2 was produced in the same manner as the seedcrystal dispersion 1 in Production Example B1 except that water wasadded in such a manner that the RHO type zeolite was 3% by mass afterproducing 10% by mass RHO zeolite dispersion.

(Production of Membrane Composite)

The seed crystal dispersion 2 was dropped onto the support, and the seedcrystal was deposited on the support by a rubbing method.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis1, an autoclave was sealed, and heated at 150° C. for 72 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 1.5/(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane composite. The RHO zeolitemembrane composite was heated from room temperature to 150° C. in 2hours, and from 150° C. to 400° C. in 20 hours, and after firing at 400°C. for 5 hours, the membrane composite was cooled to 150° C. in 20hours, and from 150° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 78 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 45 g of a 3M ammonium nitrate aqueous solution, andan autoclave was sealed and heated at 110° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution, washed with ion-exchangedwater, and then dried at 100° C. for 4 hours or more to obtain an NH₄⁺-type RHO zeolite membrane composite.

In order to convert the obtained NH₄ ⁺-type RHO zeolite membranecomposite into H⁺-type, this RHO zeolite membrane composite was fired inan electric furnace at 400° C. for 2 hours. At this time, thetemperature rise rate and the temperature drop rate up to 150° C. wereboth set at 2.5° C./min, and the temperature rise rate and thetemperature drop rate from 150° C. to 400° C. were set to 0.5° C./min toobtain an H⁺-type RHO zeolite membrane composite which is an RHO zeolitemembrane composite 4. The nitrogen atom/Al atom molar ratio of thezeolite membrane measured by XPS was 0.23, and the Si atom/Al atom molarratio was 2.92.

Example B3 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 4 described in ProductionExample B3, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed using the apparatus shown inFIG. 1.

In a pre-treatment, a mixed gas of 50% by volume H₂/50% by volume N₂ wasintroduced as a supply gas between a pressure vessel and an RHO zeolitemembrane composite 4 at 250° C., the pressure was maintained at about0.3 MPa, and the inside of a cylinder of the RHO zeolite membranecomposite 4 was set at 0.098 MPa (atmospheric pressure) and dried forabout 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite 4 was0.3 MPa. 2.4 SCCM of argon was supplied from the supply gas 9 as a sweepgas.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 4 to 150° C., 250° C., and 300° C., andthe ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen werecalculated. The results obtained are shown in Table 14. From thisresult, it was confirmed that although the ammonia separationperformance of this H⁺-type RHO zeolite membrane composite having anitrogen atom/Al atom molar ratio of 0.23 as measured by XPS slightlydecreased compared with the separation results of NH₄ ⁺-type RHO zeolitemembrane composites of Examples B1 and 2, the separation performance wasstill high. The ammonia permeance at 250° C. was 1.0×10⁻⁸[mol/(m²·s·Pa)].

TABLE 14 150° C. 250° C. 300° C. NH₃ concentration in permeated gas 52%54% 52% 5NH₃/N₂ permeance ratio 20 25 24 NH₃/H₂ permeance ratio 5 6 5

Production Example B4: Production of RHO Zeolite Membrane Composite 5

The RHO zeolite membrane composite 5 was produced by the followingmethod. As the raw material mixture for hydrothermal synthesis, the samemixture as the raw material mixture for hydrothermal synthesis 2 ofProduction Example B2 was used, and the same support and seed crystaldispersion as the support and seed crystal dispersion 1 of ProductionExample B1, respectively were used.

(Production of Membrane Composite)

A support whose inside was evacuated was immersed in this seed crystaldispersion 1 for 1 minute, and then the seed crystal was deposited onthe support by a rubbing method with the inside of the supportevacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis2, an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0L/(m²·min). Next, in order to remove a template, the obtained membranecomposite was fired by heating from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours to obtain anCs⁺-type RHO zeolite membrane composite 5. This RHO zeolite membranecomposite 5 did not use any raw material containing nitrogen atoms inthe preparation step, and the content thereof was less than 0.01 interms of the molar ratio of nitrogen atoms to Al atoms. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 58 g/m².

Reference Example B1 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 5 described in ProductionExample B4, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed using the apparatus shown inFIG. 1 in accordance with the above-described method.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and an RHO zeolite membrane composite 5 at 250° C., the pressurewas maintained at about 0.3 MPa, and the inside of a cylinder of the RHOzeolite membrane composite 2 was set at 0.098 MPa (atmospheric pressure)and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite 5 was0.3 MPa. 3.9 SCCM of argon was supplied from the supply gas 9 as a sweepgas.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 5 to 250° C. and 300° C., and the ammoniaconcentration in the obtained permeated gas and the permeance ratio ofammonia/hydrogen and ammonia/nitrogen were shown in Table 15. Theammonia permeance at 250° C. was 1.9×10⁻⁸ [mol/(m²·s·Pa)], and theammonia permeance at 300° C. was 2.0×10⁻⁸ [mol/(m²·s·Pa)]. From theresults of Table 15, it was found that this Cs⁺-type RHO zeolitemembrane essentially free of nitrogen atoms had a lower ammoniaseparation ability than the RHO zeolite membrane of any of Examples B1to 3 containing a specific amount of nitrogen atoms with respect to Alatoms determined by X-ray photoelectron spectroscopy, and had a tendencythat the separation performance greatly deteriorated when thetemperature was further raised. Accordingly, from this result, it wasfound that, when a zeolite membrane containing a specific amount ofnitrogen atoms with respect to Al atoms determined by X-rayphotoelectron spectroscopy was used, the affinity between the membraneand ammonia was increased, the ammonia was preferentially permeated, andhigh stability with respect to temperature can be achieved.

TABLE 15 250° C. 300° C. NH₃ concentration in permeated gas 49% 42%NH₃/N₂ permeance ratio 30 22 NH₃/H₂ permeance ratio 7 5

Example C [Measurement of Physical Properties and SeparationPerformance]

In the following, the physical properties and separation performance ofzeolite or a zeolite membrane composite were measured in the same manneras in Example B.

Production Example C1: Production of RHO Zeolite Membrane Composite 1, 2

RHO zeolite membrane composites 1 and 2 were produced by the followingmethod. Prior to the production of the RHO zeolite membrane composites 1and 2, a raw material mixture for hydrothermal synthesis 1, a support,and a seed crystal dispersion 1 were prepared as follows.

(Raw Material Mixture for Hydrothermal Synthesis 1)

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) weredissolved in 125.9 g of water and stirred at 80° C. for 3 hours toobtain a crown ether-alkali aqueous solution. The above-described crownether-alkali aqueous solution was added dropwise to 8.9 g of Y (FAU)zeolite (SAR=30, CBV720, manufactured by Zeolyst International) toprepare a raw material mixture for hydrothermal synthesis. The gelcomposition (molar ratio) of the obtained raw material mixture forhydrothermal synthesis 1 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.36/0.18/50/0.18.

(Support)

As a porous support, an alumina tube (outer diameter 6 mm, innerdiameter 4 mm, pore diameter 0.15 μm, manufactured by Noritake CompanyLimited) cut into a length of 80 mm, washed with water, and then driedwas used.

(Seed Crystal Dispersion 1)

23 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 6 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 5 gof CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolvedin 84 g of water, and the resulting solution was stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution.

Next, the above-described crown ether-alkali aqueous solution was addeddropwise to 30 g of FAU zeolite (SAR=30, CBV720 manufactured by ZeolystInternational), 0.6 g of RHO zeolite synthesized according to WO2015020014 was further added as a seed crystal, and the mixture wasstirred at room temperature for 2 hours to prepare a mixture. Thecomposition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18.

The mixture was aged at room temperature for 24 hours, then placed in apressure vessel and allowed to stand still in an oven at 150° C. for 72hours for hydrothermal synthesis. After this hydrothermal synthesisreaction, the reaction solution was cooled, and a produced crystal wasrecovered by filtration. The recovered crystal was dried at 100° C. for12 hours to obtain a crystal that is RHO zeolite.

The obtained RHO zeolite was pulverized by a ball mill to produce a seedcrystal dispersion. Specifically, 10 g of the above-described RHOzeolite, 300 g of φ3 mm HD Alumina Ball (manufactured by NikkatoCorporation), and 90 g of water were placed in 500 mL polyethylenebottle, and ball-milled for 6 hours to obtain a 10% by mass RHO zeolitedispersion. Water was added to the zeolite dispersion in such a mannerthat the RHO zeolite was 1% by mass to obtain a seed crystal dispersion1.

(Production of Zeolite Membrane Composite)

Next, a support whose inside was evacuated was immersed in this seedcrystal dispersion 1 for 1 minute, and then the seed crystal wasdeposited on the support by a rubbing method with the inside of thesupport evacuated.

The support with the seed crystal deposited thereon was immersed in thevertical direction in a Teflon (registered trademark) inner cylindercontaining the raw material mixture for hydrothermal synthesis, anautoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane composite. The RHO zeolitemembrane composite was heated from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 62 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Treatment with 1M ammonium nitrate aqueous solution was then repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite as an RHO zeolite membranecomposite 1.

The NH₄ ⁺-type RHO zeolite membrane composite 1 obtained was placed intoa Teflon container (registered trademark) inner cylinder (65 ml)containing 45 g of a 1M aluminum nitrate aqueous solution, and anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the NH₄ ⁺-type RHOzeolite membrane composite 1 subjected to the above-described treatmentwas taken out from the aqueous solution, washed with ion exchangedwater, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite which is an RHOzeolite membrane composite 2. The nitrogen atom/Al atom molar ratio ofthe zeolite membrane measured by XPS was 0.42, and the Si atom/Al atommolar ratio was 3.01.

Example C1 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 2 described in ProductionExample C1, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was specifically conducted in accordance withthe following method using the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volume112/60% by volume N₂ was introduced as a supply gas between a pressurevessel and the RHO zeolite membrane composite 2 at 250° C., the pressurewas maintained at about 0.3 MPa, and the inside of a cylinder of the RHOzeolite membrane composite 2 was set at 0.098 MPa (atmospheric pressure)and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass as a supply gas at 100 SCCM, and the back pressurewas set to 0.4 MPa. At this time, the differential pressure between thesupply gas side and the permeated gas side of the RHO zeolite membranecomposite 2 was 0.3 MPa. 3.9 SCCM of argon was supplied from the supplygas 9 as a sweep gas.

The mixed gas was allowed to pass while changing the temperature of theRHO zeolite membrane composite 2 to 250° C., 300° C., and 325° C., andthe ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 16. The ammonia permeance at 250° C. was 1.0×10⁻⁸ [mol/(m²·s·Pa)],and the ammonia permeance at 325° C. was 2.0×10⁻⁸ [mol/(m²·s·Pa)]. Fromthe results of Table 16, it can be seen that ammonia can be efficientlyseparated by using an NH₄ ⁺-type RHO zeolite membrane having a Siatom/Al atom molar ratio of 3.01 in XPS measurement. It was found that,in the case of this NH₄ ⁺-type RHO zeolite membrane having a Si atom/Alatom molar ratio of 3.01 as measured by XPS, when the ammoniaconcentrations of the obtained permeated gas at 250° C. and 325° C. werecompared, the change rate was almost 0%, and this zeolite membrane was aseparation membrane having excellent separation heat stability.

TABLE 16 250° C. 300° C. 325° C. NH₃ concentration in permeated gas 71%70% 71% NH₃/N₂ permeance ratio 43 59 63 NH₃/H₂ permeance ratio 15 13 13

Production Example C2: Production of RHO Zeolite Membrane Composite 3

An RHO zeolite membrane composite 3 was produced by the followingmethod. The support used was the same support as in Production ExampleC1, and the seed crystal dispersion used was the same as the seedcrystal dispersion 1 in Production Example C1.

(Mixture for Hydrothermal Synthesis 2)

The following raw material mixture for hydrothermal synthesis 2 wasprepared. 6.8 g of 18-crown-6-ether (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 2.1 g of NaOH (manufactured by Kishida ChemicalCo., Ltd.), and 4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co.,Ltd.) were dissolved in 125.9 g of water and stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution. Theabove-described crown ether-alkali aqueous solution was then addeddropwise to 8.9 g of Y-type (FAU) zeolite (SAR=30, CBV720 manufacturedby Zeolyst International) and 0.2 g of aluminum hydroxide (Al₂O₃, 53.5%by mass, manufactured by Aldrich Co., Ltd.) to prepare a raw materialmixture for hydrothermal synthesis. The gel composition (molar ratio) ofthe obtained raw material mixture for hydrothermal synthesis 2 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.040/0.36/0.18/50/0.18.

(Production of Membrane Composite)

A seed crystal dispersion 1 and a support were prepared by the samemethod as in Production Example C1, and the support whose inside wasevacuated was immersed in this seed crystal dispersion 1 for 1 minute,and then the seed crystal was deposited on the support by a rubbingmethod with the inside of the support evacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis,an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane composite. The RHO zeolitemembrane composite was heated from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 56 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Next, treatment with 1M ammonium nitrate aqueous solution was repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite.

The NH₄ ⁺-type RHO zeolite membrane composite 1 was placed into a Tefloncontainer (registered trademark) inner cylinder (65 ml) containing 50 gof a 1M aluminum nitrate aqueous solution. An autoclave was sealed andheated at 100° C. for 1 hour in a stationary state under aself-generated pressure.

After elapse of a predetermined time, after cooling, the RHO typemembrane was taken out from the aqueous solution, washed with ionexchanged water, and then dried at 100° C. for 4 hours or more to obtainan Al-treated NH₄ ⁺-type RHO zeolite membrane composite which was an RHOzeolite membrane composite 3. The nitrogen atom/Al atom molar ratio ofthe zeolite membrane measured by XPS was 0.76, and the Si atom/Al atommolar ratio was 6.65.

Example C2 <Evaluation of Membrane Separation Performance>

A separation test of a mixed gas of 12% by volume NH₃/51% by volumeN₂/37% by volume H₂ was conducted under the conditions of 250° C. and325° C. in the same manner as in Example C1 except that the RHO zeolitemembrane composite 3 described in Production Example C2 was used inplace of the RHO zeolite membrane composite 2 described in ProductionExample C1, and that 8.3 SCCM of argon was supplied as a sweep gas.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 17. The ammonia permeance at 250° C. was 1.3×10⁻⁸ [mol/(m²·s·Pa)],and the ammonia permeance at 325° C. was 2.8×10⁻⁸ [mol/(m²·s·Pa)]. Fromthe results of Table 17, it can be seen that, by using this NH₄ ⁺-typeRHO zeolite membrane having a Si atom/Al atom molar ratio of 6.65,ammonia can be separated efficiently. It was found that, in the case ofthis NH₄ ⁺-type RHO zeolite membrane having a Si atom/Al atom molarratio of 6.65 as measured by XPS, when the ammonia concentrations of theobtained permeated gas at 250° C. and 325° C. were compared, the changerate was about 5%, and this zeolite membrane was a separation membranehaving excellent separation heat stability.

TABLE 17 250° C. 325° C. NH₃ concentration in permeated gas 85% 81%NH₃/N₂ permeance ratio 408 368 NH₃/H₂ permeance ratio 132 69

Production Example C3: Production of RHO Zeolite Membrane Composite 4

An RHO zeolite membrane composite 4 was produced by the followingmethod.

An NH₄ ⁺-type RHO zeolite membrane composite obtained by the same methodas the RHO zeolite membrane composite 1 of Production Example C1 wasplaced in a Teflon container (registered trademark) inner cylinder (65ml) containing 50 g of 1M sodium nitrate aqueous solution. An autoclavewas sealed and heated at 100° C. for 1 hour in a stationary state undera self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour, followed by drying at 100° C. for 4hours or more to obtain an RHO zeolite membrane composite ion-exchangedto Na⁺-type. Next, the Na⁺-type RHO zeolite membrane obtained was placedinto a Teflon container (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M aluminum nitrate aqueous solution, and anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO typemembrane was taken out from the aqueous solution, washed with ionexchanged water, and then dried at 100° C. for 4 hours or more to obtainan Al-treated Na⁺-type RHO zeolite membrane composite which was an RHOzeolite membrane composite 4. The zeolite membrane had an Na/Al atommolar ratio of 0.05, an N atom/Al atom molar ratio of 1.21, and a Siatom/Al atom molar ratio of 7.46, as measured by XPS.

Example C3 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 4 described in ProductionExample C3, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed by the above-described methodusing the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and an RHO zeolite membrane composite 4 under a condition of 250°C., the pressure was maintained at about 0.3 MPa, and the inside of acylinder of the RHO zeolite membrane composite 4 was set at 0.098 MPa(atmospheric pressure) and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite was 0.3MPa. 8.3 SCCM of argon was supplied from the supply gas 9 as a sweepgas.

The concentration of ammonia in the permeated gas and the permeanceratio of ammonia/hydrogen and ammonia/nitrogen A are shown in Table 18.The ammonia permeance at 250° C. was 4.4×10⁻⁸ [mol/(m²·s·Pa)], and theammonia permeance at 325° C. was 1.1×10⁻⁷ [mol/(m²·s·Pa)]. From theresults of Table 18, it can be seen that ammonia can be efficientlyseparated by using an Na⁺-type RHO zeolite membrane having a Si atom/Alatom molar ratio of 7.46 in XPS measurement. It was found that, in thecase of this Na⁺-type RHO zeolite membrane having a Si atom/Al atommolar ratio of 7.46 as measured by XPS, when the ammonia concentrationsof the obtained permeated gas at 250° C. and 325° C. were compared, thechange rate was about 20%, and this zeolite membrane was a separationmembrane having slightly inferior separation heat stability, but yetexhibits high separation heat stability.

TABLE 18 250° C. 300° C. 325° C. NH₃ concentration in permeated gas 82%77% 66% NH₃/N₂ permeance ratio 259 237 230 NH₃/H₂ permeance ratio 44 3534

Production Example C4: Production of RHO Zeolite Membrane Composite 5

The RHO zeolite membrane composite 5 was produced by the followingmethod. A mixture for hydrothermal synthesis was the same as the rawmaterial mixture for hydrothermal synthesis 1 of Production Example C1,and a seed crystal dispersion was the same as the seed crystaldispersion 1.

(Support)

As a porous support, an alumina tube (outer diameter 6 mm, innerdiameter 4 mm, pore diameter 0.15 μm, manufactured by Noritake CompanyLimited) cut into a length of 40 mm, washed with water, and then driedwas used.

(Production of Membrane Composite)

A support whose inside was evacuated was immersed in this seed crystaldispersion 1 for 1 minute, and then the seed crystal was deposited onthe support by a rubbing method with the inside of the supportevacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis1, an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane F composite. This RHO zeolitemembrane composite was heated from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 52 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Next, treatment with 1M ammonium nitrate aqueous solution was repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite as an RHO zeolite membranecomposite 5.

Reference Example C1 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 5 described in ProductionExample C4, an ammonia separation test from a mixed gas of ammonia(NH₃)/hydrogen (H₂)/nitrogen (N₂) was performed using the apparatusshown in FIG. 1 in accordance with the above-described method.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and an RHO zeolite membrane composite 5 under a condition of 250°C., the pressure was maintained at about 0.3 MPa, and the inside of acylinder of the RHO zeolite membrane composite 5 was set at 0.098 MPa(atmospheric pressure) and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite was 0.3MPa. 3.9 SCCM of argon was supplied from the supply gas 9 as a sweepgas.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 19. From this result, it was found that the separation performanceof the NH₄ ⁺-type RHO zeolite membrane not treated with Al is lower thanthat of the NH₄ ⁺-type RHO zeolite membrane treated with Al. In otherwords, it was found from this result that a zeolite membrane for highlyselective separation of ammonia from a mixed gas composed of a pluralityof components including ammonia and hydrogen and/or nitrogen can bedesigned by appropriately controlling the Al atoms with respect to theSi atoms in the zeolite membrane by treating the NH₄ ⁺-type RHO zeolitemembrane with Al.

The ammonia permeance at 250° C. was 3.0×10⁻⁸ [mol/(m²·s·Pa)], and theammonia permeance at 300° C. was 2.9×10⁻⁸ [mol/(m²·s·Pa)].

TABLE 19 250° C. 300° C. NH₃ concentration in permeated gas 41% 41%NH₃/N₂ permeance ratio 15 18 NH₃/H₂ permeance ratio 4 4

Example D [Measurement of Physical Properties and SeparationPerformance]

In the following, the physical properties and separation performance ofzeolite or a zeolite membrane composite were measured in the same manneras in Example B.

Production Example D1: Production of RHO Zeolite Membrane Composite 1, 2

RHO zeolite membrane composites 1 and 2 were produced by the followingmethod. Prior to the production of the RHO zeolite membrane composites 1and 2, a raw material mixture for hydrothermal synthesis 1, a support,and a seed crystal dispersion 1 were prepared as follows.

(Raw Material Mixture for Hydrothermal Synthesis 1)

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) weredissolved in 125.9 g of water and stirred at 80° C. for 3 hours toobtain a crown ether-alkali aqueous solution. The above-described crownether-alkali aqueous solution was added dropwise to 8.9 g of Y (FAU)zeolite (SAR=30, CBV720, manufactured by Zeolyst International) toprepare a raw material mixture for hydrothermal synthesis. The gelcomposition (molar ratio) of the obtained raw material mixture forhydrothermal synthesis 1 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.36/0.18/50/0.18.

(Support)

As a porous support, an alumina tube (outer diameter 6 mm, innerdiameter 4 mm, pore diameter 0.15 μm, manufactured by Noritake CompanyLimited) cut into a length of 80 mm, washed with water, and then driedwas used.

(Seed Crystal Dispersion 1)

23 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 6 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 5 gof CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolvedin 84 g of water, and the resulting solution was stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution.

Next, the above-described crown ether-alkali aqueous solution was addeddropwise to 30 g of FAU zeolite (SAR=30, CBV720 manufactured by ZeolystInternational), 0.6 g of RHO zeolite synthesized according to WO2015020014 was further added as a seed crystal, and the mixture wasstirred at room temperature for 2 hours to prepare a mixture. Thecomposition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18.

The mixture was aged at room temperature for 24 hours, then placed in apressure vessel and allowed to stand still in an oven at 150° C. for 72hours for hydrothermal synthesis. After this hydrothermal synthesisreaction, the reaction solution was cooled, and a produced crystal wasrecovered by filtration. The recovered crystal was dried at 100° C. for12 hours to obtain a crystal that is RHO zeolite.

The obtained RHO zeolite was pulverized by a ball mill to produce a seedcrystal dispersion. Specifically, 10 g of the above-described RHOzeolite, 300 g of p 3 mm HD Alumina Ball (manufactured by NikkatoCorporation), and 90 g of water were placed in 500 mL polyethylenebottle, and ball-milled for 6 hours to obtain a 10% by mass RHO zeolitedispersion. Water was added to the zeolite dispersion in such a mannerthat the RHO zeolite was 1% by mass to obtain a seed crystal dispersion1.

(Production of Zeolite Membrane Composite)

Next, a support whose inside was evacuated was immersed in this seedcrystal dispersion 1 for 1 minute, and then the seed crystal wasdeposited on the support by a rubbing method with the inside of thesupport evacuated.

The support with the seed crystal deposited thereon was immersed in thevertical direction in a Teflon (registered trademark) inner cylindercontaining the raw material mixture for hydrothermal synthesis, anautoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane composite. The RHO zeolitemembrane composite was heated from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 62 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the above-describedtreatment was performed, and the RHO zeolite membrane compositesubjected to the above-described treatment was taken out from theaqueous solution and washed with 100° C. ion exchange hot water for 1hour.

Treatment with 1M ammonium nitrate aqueous solution was then repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite as an RHO zeolite membranecomposite 1.

The NH₄ ⁺-type RHO zeolite membrane composite 1 obtained was placed intoa Teflon container (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M sodium nitrate aqueous solution. An autoclavewas sealed and heated at 100° C. for 1 hour in a stationary state undera self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour, followed by drying at 100° C. for 4hours or more to obtain an RHO zeolite membrane composite ion-exchangedto Na⁺-type. Next, the Na⁺-type RHO zeolite membrane obtained was placedinto a Teflon container (registered trademark) inner cylinder (65 ml)containing 50 g of a 1M aluminum nitrate aqueous solution, and anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO typemembrane was taken out from the aqueous solution, washed with ionexchanged water, and then dried at 100° C. for 4 hours or more to obtainan Al-treated Na⁺-type RHO zeolite membrane composite which was an RHOzeolite membrane composite 2. The alkali metal/Al atom molar ratio ofthe zeolite membrane of the zeolite membrane composite measured by XPSwas 0.05, the N atom/Al atom molar ratio was 1.21, and the Si atom/Alatom molar ratio was 7.46.

Example D1 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 2 described in ProductionExample D1, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was specifically conducted in accordance withthe following method using the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and the RHO zeolite membrane composite 2 under a condition of250° C., the pressure was maintained at about 0.3 MPa, and the inside ofa cylinder of the RHO zeolite membrane composite 2 was set at 0.098 MPa(atmospheric pressure) and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass as a supply gas at 100 SCCM, and the back pressurewas set to 0.4 MPa. At this time, the differential pressure between thesupply gas side and the permeated gas side of the RHO zeolite membranecomposite was 0.3 MPa. 8.3 SCCM of argon was supplied from the supplygas 9 as a sweep gas.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen are shown inTable 20. From the results of Table 20, it can be seen that ammonia canbe efficiently separated by using an Na⁺-type RHO zeolite membrane. Itwas confirmed that the Na⁺-type RHO zeolite membrane treated with Alunder a high temperature condition can separate ammonia with highselectivity. The ammonia permeance at 250° C. was 4.4×10⁻⁸[mol/(m²·s·Pa)], and from the comparison with the RHO zeolite membranecomposite 3 containing no alkali metal and having an equivalent Natom/Al atom molar ratio and Si atom/Al atom molar ratio of the presentReference Example D1, it was found that when an alkali metal atom wascontained, an equivalent high concentration of ammonia can be recoveredwith high permeability.

TABLE 20 250° C. NH₃ concentration in permeated gas 82% NH₃/N₂ permeanceratio 259 NH₃/H₂ permeance ratio 44

Production Example D2: Production of RHO Zeolite Membrane Composite 3

An RHO zeolite membrane composite 3 was produced by the followingmethod. The support used was the same support as in Production ExampleD1, and the seed crystal dispersion used was the same as the seedcrystal dispersion 1 in Production Example D1.

(Mixture for Hydrothermal Synthesis 2)

The following raw material mixture for hydrothermal synthesis 2 wasprepared.

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) weredissolved in 125.9 g of water and stirred at 80° C. for 3 hours toobtain a crown ether-alkali aqueous solution. The above-described crownether-alkali aqueous solution was then added dropwise to 8.9 g of Y-type(FAU) zeolite (SAR=30, CBV720 manufactured by Zeolyst International) and0.2 g of aluminum hydroxide (Al₂O₃, 53.5% by mass, manufactured byAldrich Co., Ltd.) to prepare a raw material mixture for hydrothermalsynthesis. The gel composition (molar ratio) of the obtained rawmaterial mixture for hydrothermal synthesis 2 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.040/0.36/0.18/50/0.18.

(Production of Membrane Composite)

A seed crystal and a support were prepared by the same method as inProduction Example D1, and the support whose inside was evacuated wasimmersed in this seed crystal dispersion 1 for 1 minute, and then theseed crystal was deposited on the support by a rubbing method with theinside of the support evacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis2, an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired to obtain an RHO zeolite membrane composite. The RHO zeolitemembrane composite was heated from room temperature to 100° C. in 2hours, and from 100° C. to 300° C. in 20 hours, and after firing at 300°C. for 5 hours, the membrane composite was cooled to 100° C. in 20hours, and from 100° C. to room temperature in 2 hours. The weight ofthe RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 56 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 50 g of a 1M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 100° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution and washed with 100° C. ionexchanged hot water for 1 hour.

Next, treatment with 1M ammonium nitrate aqueous solution was repeated 5times, followed by drying at 100° C. for 4 hours or more to obtain anNH₄ ⁺-type RHO zeolite membrane composite.

The NH₄ ⁺-type RHO zeolite membrane composite 1 was placed into a Tefloncontainer (registered trademark) inner cylinder (65 ml) containing 50 gof a 1M aluminum nitrate aqueous solution. An autoclave was sealed andheated at 100° C. for 1 hour in a stationary state under aself-generated pressure.

After elapse of a predetermined time, after cooling, the NH₄ ⁺-type RHOzeolite membrane composite subjected to the above-described treatmentwas taken out from the aqueous solution, washed with ion exchangedwater, and then dried at 100° C. for 4 hours or more to obtain anAl-treated NH₄ ⁺-type RHO zeolite membrane composite which was an RHOzeolite membrane composite 3. The N atom/Al atom molar ratio of thezeolite membrane measured by XPS was 0.76, and the Si atom/Al atom molarratio was 6.65. Alkali metal was not detected.

Reference Example D1 <Evaluation of Membrane Separation Performance>

A separation test of a mixed gas of 12% by volume NH₃/51% by volumeN₂/37% by volume H₂ was conducted under the conditions where thetemperature of the RHO zeolite membrane composite 3 was 250° C. in thesame manner as in Example D1 except that the RHO zeolite membranecomposite 3 described in Production Example D2 was used in place of theRHO zeolite membrane composite 2 described in Production Example D1.

The ammonia concentration in the obtained permeated gas and thepermeance ratio of ammonia/hydrogen and ammonia/nitrogen were shown inTable 21. From the results in Table 21, it can be seen that ammonia canbe efficiently separated by using an NH₄ ⁺-type RHO zeolite membrane. Itwas also confirmed that an RHO membrane produced using a gel compositionwith an increased Al content could separate ammonia with higherselectivity even under high temperature conditions. However, the ammoniapermeance at 250° C. was 1.3×10⁻⁸ [mol/(m²·s·Pa)], and it was found thatthe permeability was lower than that of the RHO zeolite membranecomposite 2 containing an alkali metal.

TABLE 21 250° C. NH₃ concentration in permeated gas 85% NH₃/N₂ permeanceratio 408 NH₃/H₂ permeance ratio 132

Production Example D3: Production of RHO Zeolite Membrane Composite 4

An RHO zeolite membrane composite 4 was produced by the followingmethod.

(Mixture for Hydrothermal Synthesis 2)

The following raw material mixture for hydrothermal synthesis 2 wasprepared. 6.8 g of 18-crown-6-ether (manufactured by Tokyo ChemicalIndustry Co., Ltd.), 2.1 g of NaOH (manufactured by Kishida ChemicalCo., Ltd.), and 4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co.,Ltd.) were dissolved in 125.9 g of water and stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution. Theabove-described crown ether-alkali aqueous solution was then addeddropwise to 8.9 g of Y-type (FAU) zeolite (SAR=30, CBV720 manufacturedby Zeolyst International) and 0.2 g of aluminum hydroxide (Al₂O₃, 53.5%by mass, manufactured by Aldrich Co., Ltd.) to prepare a raw materialmixture for hydrothermal synthesis. The gel composition (molar ratio) ofthe obtained raw material mixture for hydrothermal synthesis 2 wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.040/0.36/0.18/50/0.18.

(Production of Membrane Composite)

A seed crystal dispersion 1 and a support were prepared by the samemethod as in Production Example D1, and the support whose inside wasevacuated was immersed in this seed crystal dispersion 1 for 1 minute,and then the seed crystal was deposited on the support by a rubbingmethod with the inside of the support evacuated.

Next, the support with the seed crystal deposited thereon was immersedin the vertical direction in a Teflon (registered trademark) innercylinder containing the raw material mixture for hydrothermal synthesis2, an autoclave was sealed, and heated at 160° C. for 24 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washingwith ion exchanged water, dried at 100° C. for 5 hours or more. Afterdrying, the air permeation amount in an as-made state was 0.0/L(m²·min).Next, in order to remove a template, the obtained membrane composite wasfired by heating from room temperature to 100° C. in 2 hours, and from100° C. to 300° C. in 20 hours, and after firing at 300° C. for 5 hours,the membrane composite was cooled to 100° C. in 20 hours, and from 100°C. to room temperature in 2 hours to obtain an Cs⁺-type RHO zeolitemembrane composite 4. As described above, since the Cs⁺-type RHO zeolitemembrane composite 4 was not subjected to an ion exchange treatment stepafter forming the zeolite membrane, the ion pair at an Al site of thezeolite was essentially an alkali metal (Cs and Na) cation. The weightof the RHO zeolite crystallized on the support determined from thedifference between the weight of the zeolite membrane composite and theweight of the support after firing was 58 g/m². The alkali metal/Al atommolar ratio of the zeolite membrane of the zeolite membrane compositemeasured by XPS was 0.073.

Reference Example D2 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 4 described in ProductionExample D3, an ammonia separation test from a mixed gas ofammonia/hydrogen/nitrogen was performed by the above-described methodusing the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 10% by volume NH₃/30% by volumeH₂/60% by volume N₂ was introduced as a supply gas between a pressurevessel and an RHO zeolite membrane composite 4 at 250° C., the pressurewas maintained at about 0.3 MPa, and the inside of a cylinder of the RHOzeolite membrane composite 4 was set at 0.098 MPa (atmospheric pressure)and dried for about 120 minutes.

A mixed gas of 12% by volume NH₃/51% by volume N₂/37% by volume H₂ wasthen allowed to pass at 100 SCCM, and the back pressure was set to 0.4MPa. At this time, the differential pressure between the supply gas sideand the permeated gas side of the RHO zeolite membrane composite 4 was0.3 MPa.

Table 22 shows the ammonia concentration in the obtained permeated gasand the permeance ratio of ammonia/hydrogen and ammonia/nitrogen, bysetting the temperature of the RHO zeolite membrane composite 4 to 250°C. and circulating a mixed gas. The ammonia permeance at 250° C. was1.9×10⁻⁸ [mol/(m²·s·Pa)]. From these results, it was found that thepresent Cs⁺-type RHO zeolite membrane in which the ion pair at an Alsite of the zeolite essentially was an alkali metal cation because noion exchange treatment step was performed after the formation of thezeolite membrane had a slightly lowered ammonia separation performancethan the RHO zeolite membrane composites 2 and 3, although the ammoniapermeability is slightly improved as compared with the RHO zeolitemembrane composite 3. Specifically, from this result, it was found thata zeolite membrane that can not only highly selectively separate ammoniafrom a mixed gas composed of a plurality of components including ammoniaand hydrogen and/or nitrogen, but also improve the ammonia permeabilitycan be designed by appropriately controlling the molar ratio of alkalimetal atoms to Al atoms in the zeolite.

TABLE 22 250° C. NH₃ concentration in permeated gas 49% NH₃/N₂ permeanceratio 30 NH₃/H₂ permeance ratio 7

Example E [Measurement of Physical Properties and SeparationPerformance]

In the following, among measurements of physical properties of zeoliteor a zeolite membrane composite, XRD measurement was carried out underthe same conditions as in Example B, and the separation performance andthe like were measured in the same manner as in Example B.

(1) Measurement of Thermal Expansion Coefficient

The thermal expansion coefficient of zeolite was determined by a hightemperature XRD measurement method under the following conditions.

(Specifications of High Temperature XRD Measurement Apparatus)

TABLE 23 Apparatus name New D8 ADVANCE manufactured by BrukerCorporation Optical system Bragg-Brentano optical system OpticalIncident side Enclosed X-ray tube (CuKα) system Sober Slit (2.5°)specifications Divergence Slit (Variable Slit) Sample stageHigh-temperature sample stage HTK1200 Light-receiving Semiconductorarray detector side (Lynx Eye) Ni-filter Soller Slit (2.5°) Goniometer280 mm radius

(Measurement Conditions)

TABLE 24 X-ray output 40 kV (CuKα) 40 mA Scanning axis θ/2θ Scanningrange (2θ) 5.0-70.0° Measurement mode Continuous Read width 0.02°Counting time 19.2 sec (0.1 sec × 192 ch) Automatic variable slit * 6 mm(irradiation width)

Measurement atmosphere: Air

Temperature rise condition: 20° C./min

Measurement method: XRD measurement was carried out after holding at themeasurement temperature for 5 minutes.

Measurement data was subjected to fixed slit correction using a variableslit.

Calculation method of change rate of thermal expansion coefficient:

Change rate of thermal expansion coefficient=(crystal lattice constantmeasured at predetermined temperature)+(crystal lattice constantmeasured at 30° C.)−1  (1)

Example E1 (Production of RHO Zeolite)

RHO zeolite was synthesized as follows.

23 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 6 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 5 gof CsOH H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolvedin 84 g of water, and the obtained solution was stirred at 80° C. for 3hours to obtain a crown ether-alkali aqueous solution.

The above-described crown ether-alkali aqueous solution was addeddropwise to 30 g of FAU zeolite (SAR=30, CBV720 manufactured by ZeolystInternational), and further, 0.6 g of RHO zeolite synthesized accordingto WO 2015020014 was added as a seed crystal and stirred at roomtemperature for 2 hours to prepare a raw material mixture forhydrothermal synthesis. The gel composition (molar ratio) of thismixture was as follows.

SiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.30/0.06/10/0.18.

This raw material mixture for hydrothermal synthesis was aged at roomtemperature for 24 hours, then placed in a pressure vessel and allowedto stand still in an oven at 150° C. for 72 hours for hydrothermalsynthesis. After this hydrothermal synthesis reaction, a reactionsolution was cooled, and a produced crystal was recovered by filtration.The recovered crystal was dried at 100° C. for 12 hours. As a result ofmeasuring the thermal expansion coefficient of the obtained RHO zeolite,the change rate of the thermal expansion coefficient at 200° C. withrespect to 30° C. was −1.55%, the change rate of the thermal expansioncoefficient at 300° C. with respect to 30° C. was 0.02%, and the changerate of the thermal expansion coefficient at 400° C. with respect to 30°C. was −0.01%, and it was confirmed that there was almost no thermalexpansion or contraction compared to the thermal expansion coefficientat 30° C.

Example E2 <Preparation of RHO Zeolite Membrane Composite 1>

A porous support-RHO zeolite membrane composite was prepared byhydrothermal synthesis of RHO zeolite directly on a porous support. As aporous support, an alumina tube (outer diameter 6 mm, pore diameter 0.15μm, manufactured by Noritake Company Limited) cut into a length of 40mm, washed with water, and then dried was used.

RHO zeolite synthesized by the method described in Example E1 pulverizedwith a ball mill was used as a seed crystal on the porous support.

Ball milling was carried out as follows. 10 g of the above-described RHOzeolite for seed crystal, 300 g of φ3 mm HD Alumina Ball (manufacturedby Nikkato Corporation), and 90 g of water were placed in 500 mLpolyethylene bottle, and ball-milled for 6 hours to obtain a 10% by massRHO zeolite dispersion. Water was added to the zeolite dispersion insuch a manner that the RHO zeolite was 3% by mass to obtain a seedcrystal dispersion.

This seed crystal dispersion was dropped onto the support, and the seedcrystal was deposited on the support by a rubbing method.

Next, the following raw material mixture for hydrothermal synthesis wasprepared.

6.8 g of 18-crown-6-ether (manufactured by Tokyo Chemical Industry Co.,Ltd.), 2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and4.2 g of CsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) 6.8 g of18-crown-6-ether (manufactured by Tokyo Chemical Industry Co., Ltd.),2.1 g of NaOH (manufactured by Kishida Chemical Co., Ltd.), and 4.2 g ofCsOH.H₂O (manufactured by Mitsuwa Chemical Co., Ltd.) were dissolved in125.9 g of water and stirred at 80° C. for 3 hours to obtain a crownether-alkali aqueous solution. The above-described crown ether-alkaliaqueous solution was then added dropwise to 8.9 g of Y-type (FAU)zeolite (SAR=30, CBV720 manufactured by Zeolyst International) toprepare a raw material mixture for hydrothermal synthesis. The gelcomposition (molar ratio) of the obtained raw material mixture forhydrothermal synthesis wasSiO₂/Al₂O₃/NaOH/CsOH/H₂O/18-crown-6-ether=1/0.033/0.36/0.18/50/0.18.

The support with the seed crystal deposited thereon was immersed in thevertical direction in a Teflon (registered trademark) inner cylindercontaining the raw material mixture for hydrothermal synthesis, anautoclave was sealed, and heated at 150° C. for 72 hours under aself-generated pressure.

After elapse of a predetermined time, after cooling, a support-zeolitemembrane composite was taken out from an autoclave, and after washing,dried at 100° C. for 5 hours or more. After drying, the air permeationamount in an as-made state was 1.5 L/(m²·min). Next, in order to removea template, the obtained membrane composite was fired to obtain an RHOzeolite membrane composite. The weight of the RHO zeolite crystallizedon the support determined from the difference between the weight of thezeolite membrane composite and the weight of the support after firingwas 78 g/m².

Next, the RHO zeolite membrane composite after removal of the templatewas placed into a Teflon container (registered trademark) inner cylinder(65 ml) containing 45 g of a 3M ammonium nitrate aqueous solution. Anautoclave was sealed and heated at 110° C. for 1 hour in a stationarystate under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution, washed with water, and thendried at 100° C. for 4 hours or more to obtain an NH₄ ⁺-type RHO zeolitemembrane composite.

In order to convert the NH₄ ⁺-type RHO zeolite membrane composite intoH⁺-type, this RHO zeolite membrane composite was fired in an electricfurnace at 400° C. for 2 hours. At this time, the temperature rise rateand the temperature drop rate up to 150° C. were both set at 2.5°C./min, and the temperature rise rate and the temperature drop rate from150° C. to 400° C. were set to 0.5° C./min to obtain an H⁺-type RHOzeolite membrane composite. Hereinafter, the produced RHO zeolitemembrane composite is referred to as “RHO zeolite membrane composite 1”.

Example E3 (Evaluation of Membrane Separation Performance)

Using the RHO zeolite membrane composite 1 described in Example E2, anammonia separation test from a mixed gas of ammonia/hydrogen/nitrogenwas performed using the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 50% H₂/50% N₂ was introduced as asupply gas 7 between a pressure vessel 2 and a zeolite membranecomposite 1 at 250° C., the pressure was maintained at about 0.3 MPa,and the inside of a cylinder of the zeolite membrane composite 1 was setat 0.098 MPa (atmospheric pressure) and dried for about 120 minutes.

A mixed gas of 12% ammonia/51% nitrogen/37% hydrogen was then allowed topass at 100 SCCM, and the back pressure was set to 0.4 MPa. At thistime, the differential pressure between the supply gas 7 side and thepermeated gas 8 side of the RHO zeolite membrane composite 1 was 0.3MPa.

Table 25 shows the ammonia concentration in the obtained permeated gasand the permeance ratio of ammonia/hydrogen and ammonia/nitrogen, bychanging the temperature of the RHO zeolite membrane composite 1 to from150° C. to 300° C. and circulating the mixed gas. From these results, itwas confirmed that ammonia could be separated with high selectivitywithout causing any gaps or defects between zeolite particles due to thesmall thermal expansion or contraction of the RHO zeolite under hightemperature conditions. The ammonia permeance at 250° C. was 1.0×10⁻⁸[mol/(m²·s·Pa)].

Accordingly, the zeolite membrane composite of the present inventionshows that ammonia can be stably and highly selectively separated evenunder high temperature conditions by carrying out synthesis usingzeolite whose change rate of thermal expansion is within a specificrange as a seed crystal.

TABLE 25 150° C. 250° C. 300° C. NH₃ concentration in permeated gas 52%54% 52% NH₃/N₂ permeance ratio 20 25 24 NH₃/H₂ permeance ratio 5 6 5

Example E4 <Na⁺-Type RHO Synthesis>

For the Na⁺-type RHO zeolite, hydrothermal synthesis was carried out bythe method described in “Microporous and Mesoporous Materials 132 (2010)352-356)”. After the hydrothermal synthesis reaction, a reactionsolution was cooled and a produced crystal was recovered by filtration.The recovered crystal was dried at 100° C. for 12 hours. The results ofmeasuring the thermal expansion coefficient of the obtained RHO zeoliteare shown in FIG. 2. It was confirmed that the thermal expansioncoefficient of the Na⁺-type RHO can be approximated to a linear linewith respect to temperature. From this approximate expression, thechange rate of thermal expansion coefficient at 300° C. with respect to30° C. was estimated to be 0.23%, and the change rate of thermalexpansion coefficient at 400° C. with respect to 30° C. was estimated tobe 0.33%.

Example E5 <Synthesis of RHO Zeolite Membrane Composite 2>

An NH₄ ⁺-type RHO zeolite membrane composite was obtained in the samemanner as in Example E2 except that a support with a seed crystaldeposited was immersed in the vertical direction in a Teflon (registeredtrademark) inner cylinder containing a raw material mixture forhydrothermal synthesis, an autoclave was sealed, and heated at 150° C.for 72 hours under a self-generated pressure.

The NH₄ ⁺-type RHO zeolite membrane composite after removal of thetemplate was placed into a Teflon container (registered trademark) innercylinder (65 ml) containing 45 g of a 1M aluminum nitrate aqueoussolution. An autoclave was sealed and heated at 100° C. for 1 hour in astationary state under a self-generated pressure.

After elapse of a predetermined time, after cooling, the RHO membranewas taken out from the aqueous solution, washed with water, and thendried at 100° C. for 4 hours or more to obtain an Al-treated NH₄ ⁺-typeRHO zeolite membrane composite.

The obtained composite was again placed in a Teflon container(registered trademark) inner cylinder (65 ml) containing 45 g of a 1Msodium nitrate aqueous solution. An autoclave was sealed and heated at100° C. for 1 hour in a stationary state under a self-generatedpressure.

After elapse of a predetermined time, after cooling, the RHO zeolitemembrane was taken out from the aqueous solution, washed with water, andthen dried at 100° C. for 4 hours or more to obtain an RHO zeolitemembrane composite ion-exchanged to Na⁺-type after an Al treatment.

Hereinafter, a produced RHO zeolite membrane composite which ision-exchanged to Na⁺-type after an Al treatment is referred to as “RHOzeolite membrane composite 2”.

Example E6 <Evaluation of Membrane Separation Performance>

Using the RHO zeolite membrane composite 2 described in Example E5, anammonia separation test from a mixed gas of ammonia/hydrogen/nitrogenwas performed using the apparatus shown in FIG. 1.

In a pre-treatment, a mixed gas of 50% H₂/50% N₂ was introduced as asupply gas 7 between a pressure vessel 2 and a zeolite membranecomposite 1 at 250° C., the pressure was maintained at about 0.3 MPa,and the inside of a cylinder of the zeolite membrane composite was setat 0.098 MPa (atmospheric pressure) and dried for about 120 minutes.

A mixed gas of 12% ammonia/51% nitrogen/37% hydrogen was then allowed topass at 100 SCCM, and the back pressure was set to 0.4 MPa. At thistime, the differential pressure between the supply gas 7 side and thepermeated gas 8 side of the RHO zeolite membrane composite 2 was 0.3MPa.

Table 26 shows the ammonia concentration in the obtained permeated gasand the permeance ratio of ammonia/hydrogen and ammonia/nitrogen, bychanging the temperature of the RHO zeolite membrane composite 2 to 50°C. and 250° C. and circulating the mixed gas. From these results, it wasconfirmed that ammonia could be separated with high selectivity withoutcausing any gaps or defects between zeolite particles due to the smallthermal expansion or contraction of the RHO zeolite under hightemperature conditions. The ammonia permeance at 250° C. was 2.0×10⁻⁸[mol/(m²·s·Pa)].

Accordingly, it was confirmed that an RHO membrane composite stablyseparated ammonia under high temperature conditions when the change rateof thermal expansion coefficient of zeolite constituting the zeolitemembrane composite was in a specific range.

TABLE 26 100° C. 250° C. NH₃ concentration in permeated gas 60% 56%5NH₃/N₂ permeance ratio 29 31 NH₃/H₂ permeance ratio 7 6

Example E7 <Production of MFI Zeolite>

MFI zeolite was synthesized as follows.

To a mixture of 13.65 g of a 50% by weight NaOH aqueous solution and 101g of water, 0.15 g of sodium aluminate (containing Al₂O₃-62.2% by mass)was added and stirred at room temperature for 10 minutes. To this, 32.3g of colloidal silica (Snowtech-40, manufactured by Nissan Chemical Co.,Ltd.) was added and stirred for 5 hours at 50 degrees to obtain a rawmaterial mixture for hydrothermal reaction. The composition (molarratio) of this raw material mixture for hydrothermal reaction isSiO₂/Al₂O₃/NaOH/H₂O=3.05/0.013/0.193/100, SiO₂/Al₂O₃=239.

This raw material mixture for hydrothermal synthesis was placed in apressure vessel, and hydrothermal synthesis was carried out in an ovenat 180° C. for 30 hours while stirring at 15 rpm. After thishydrothermal synthesis reaction, a reaction solution was cooled and aproduced crystal was recovered by filtration. The recovered crystal wasdried at 100° C. for 12 hours. As a result of measuring the thermalexpansion coefficient in the c-axis direction of the obtained MFIzeolite, the change rate of the thermal expansion coefficient at 200° C.with respect to 30° C. was 0.13%, the change rate of the thermalexpansion coefficient at 300° C. with respect to 30° C. was 0.15%, andthe change rate of the thermal expansion coefficient at 400° C. withrespect to 30° C. was 0.13% (each in the c-axis direction), and it wasconfirmed that zeolite was expanded as compared with the case of 30° C.

Example E8 <Preparation of MFI Zeolite Membrane Composite>

First, a raw material mixture for hydrothermal synthesis was prepared bythe following method.

To a mixture of 13.65 g of a 50% by weight NaOH aqueous solution and 101g of water, 0.15 g of sodium aluminate (containing Al₂O₃-62.2% by mass)was added and stirred at room temperature for 10 minutes. To this, 32.3g of colloidal silica (Snowtech-40, manufactured by Nissan Chemical Co.,Ltd.) was added and stirred for 5 hours at 50 degrees to obtain a rawmaterial mixture for hydrothermal reaction. The composition (molarratio) of this raw material mixture for hydrothermal reaction isSiO₂/Al₂O₃/NaOH/H₂O=3.05/0.013/0.193/100, SiO₂/Al₂O₃=239.

ZSM5 zeolite (manufactured by Tosoh Corporation, HSZ-800 series 822H0A)ground in a mortar was prepared as a seed crystal, a porous support wasimmersed in an aqueous solution (ZSM5 seed crystal aqueous solution) inwhich the concentration of the seed crystal was about 0.4% by mass, andthe support was dried at 70° C. for 1 hour, immersed again in the ZSM5seed crystal solution for 1 minute, and then dried at 70° C. for 1 hourto deposit the seed crystal. The mass of the deposited seed crystal wasabout 0.0016 g. As the porous support, an alumina tube BN1 (outerdiameter 6 mm, inner diameter 4 mm) manufactured by Noritake CompanyLimited cut into a length of 80 mm, washed with an ultrasonic cleaner,and then dried was used. Three porous supports having a seed crystaldeposited thereon were prepared by the above-described method.

Three supports with the seed crystal deposited thereon were eachimmersed in the vertical direction in the above-described Teflon(registered trademark) inner cylinder (200 ml) containing theabove-described aqueous reaction mixture, an autoclave was sealed, andheated at 180° C. for 30 hours in a stationary state under aself-generated pressure. After elapse of a predetermined time, aftercooling, the support-zeolite membrane composite was taken out from thereaction mixture, washed, and dried at 100° C. for 3 hours to obtain anMFI zeolite membrane composite 2. The mass of MFI zeolite crystallizedon the support was from 0.26 to 0.28 g. The air permeation amount of themembrane composite after firing was from 0.0 to 0.1 cm³/min.

Example E9 <Evaluation of Membrane Separation Performance>

The temperature of the MFI zeolite membrane composite 2 described inExample E8 was changed from 100° C. to 250° C. and a mixed gas of 12%ammonia/51% nitrogen/37% hydrogen was allowed to pass at a flow rate of100 SCCM, and the concentration of ammonia and the permeance ratio ofammonia/hydrogen and ammonia/nitrogen of the obtained permeated gas areshown in Table 27. Even when the temperature was changed from 150° C. to250° C., it was confirmed that ammonia permeated through the membranewith high selectivity. Accordingly, since it was confirmed that ammoniacould be separated with high selectivity without any gaps or defectsbetween zeolite particles even under high temperature conditions, thethermal expansion coefficient of zeolite is considered to be comparableto that of the RHO zeolite membrane composite. The ammonia permeance at250° C. was 7.5×10⁻⁸ [mol/(m²·s·Pa)].

TABLE 27 100° C. 150° C. 200° C. 250° C. NH₃ concentration in permeatedgas 46% 44% 46% 45% NH₃/N₂ permeance ratio 18 18 23 23 NH₃/H₂ permeanceratio 5 4 5 5

Reference Example E1 <Production of CHA Zeolite>

CHA zeolite was synthesized as follows.

To a mixture of 0.6 g of NaOH (manufactured by Kishida Chemical Co.,Ltd.), 1.1 g of KOH (manufactured by Kishida Chemical Co., Ltd.), and 10g of water, 0.5 g of aluminum hydroxide (containing Al₂O₃-53.5% by mass,manufactured by Aldrich Co., Ltd.) was added and dissolved by stirringto obtain a transparent solution. To this, 5.4 g of a 25% by massaqueous solution of N,N,N-trimethyl-1-adamantanammonium hydroxide(hereinafter, referred to as “TMADAOH”) was added as an organictemplate, and then 12 g of colloidal silica (Snowtech-40, manufacturedby Nissan Chemical Co., Ltd.) was added and stirred for 2 hours toobtain a raw material mixture for hydrothermal synthesis. Thecomposition (molar ratio) of this mixture isSiO₂/Al₂O₃/NaOH/KOH/H₂O/TMADAOH=1/0.033/0.2/0.2/15/0.08, SiO₂/Al₂O₃=30.

This raw material mixture for hydrothermal synthesis was placed in apressure vessel and in an oven at 190° C. for 15 hours while stirring at15 rpm for hydrothermal synthesis. After this hydrothermal synthesisreaction, the reaction solution was cooled, and a produced crystal wasrecovered by filtration. The recovered crystal was dried at 100° C. for12 hours. As a result of measuring the thermal expansion coefficient ofthe obtained CHA zeolite, The change rate of thermal expansioncoefficient at 200° C. with respect to 30° C. was −0.13%, the changerate of thermal expansion coefficient at 300° C. with respect to 30° C.was −0.30%, and the change rate of thermal expansion coefficient at 400°C. with respect to 30° C. was −0.40% (both in the c-axis direction), andit was confirmed that the zeolite contracted compared to 30° C.

Reference Example E2 <Production of CHA Zeolite Membrane Composite>

First, a raw material mixture for hydrothermal synthesis was prepared asfollows.

To a mixture of 1.45 g of 1 mol/L-NaOH aqueous solution, 5.78 g of 1mol/L-KOH aqueous solution, and 114.6 g of water, 0.19 g of aluminumhydroxide (containing Al₂O₃-53.5% by mass, manufactured by Aldrich Co.,Ltd.) was added and dissolved by stirring to obtain a transparentsolution. To this, 2.43 g of a 25% by mass aqueous solution of TMADAOHwas added as an organic template, and then 10.85 g of colloidal silica(Snowtech-40, manufactured by Nissan Chemical Co., Ltd.) was added andstirred for 2 hours to obtain a raw material mixture for hydrothermalsynthesis. The composition (molar ratio) of this mixture wasSiO₂/Al₂O₃/NaOH/KOH/H₂O/TMADAOH=1/0.018/0.02/0.08/100/0.04,SiO₂/Al₂O₃=58.

As a porous support, an alumina tube BN1 (outer diameter 6 mm, innerdiameter 4 mm) manufactured by Noritake Company Limited cut into alength of 80 mm, washed with an ultrasonic cleaner, and then dried wasused.

As a seed crystal, CHA zeolite obtained by filtering, washing withwater, and drying a crystal having a gel composition (molar ratio) ofSiO₂/Al₂O₃/NaOH/KOH/H₂O/TMADAOH=1/0.033/0.1/0.06/20/0.07 obtained byhydrothermal synthesis at 160° C. for 2 days was used. The seed crystalgrain size was about from 0.3 to 3 μm.

The support was immersed in a solution in which the seed crystal wasdispersed in water to a concentration of about 1% by mass (CHA seedcrystal aqueous solution) for 1 minute, and then dried at 100° C. for 1hour to deposit the seed crystal. The mass of the deposited seed crystalwas about 0.001 g.

Three supports with the seed crystal deposited thereon was immersed inthe vertical direction in a Teflon (registered trademark) inner cylinder(200 ml) containing the above-described aqueous reaction mixture, anautoclave was sealed, and heated at 180° C. for 72 hours in a stationarystate under a self-generated pressure. After elapse of a predeterminedtime, after cooling, the support-zeolite membrane composite was takenout from the reaction mixture, washed, and dried at 100° C. for 3 hours.

The dried membrane composite was fired in air in an electric furnace at450° C. for 10 hours and at 500° C. for 5 hours. At this time, thetemperature rise rate and the temperature drop rate from roomtemperature to 450° C. were both 0.5° C./min, and the temperature riserate and the temperature drop rate from 450° C. to 500° C. were both0.1° C./min. The mass of the CHA zeolite crystallized on the support,which was determined from the difference between the mass of themembrane composite and the mass of the support after firing, was aboutfrom 0.279 to 0.289 g. The air permeation amount of the membranecomposite after firing was from 2.4 to 2.9 cm³/min.

Hereinafter, the produced CHA zeolite membrane composite is referred toas “CHA zeolite membrane composite 3”.

Reference Example E3 <Evaluation of Membrane Separation Performance>

The temperature of the CHA zeolite membrane composite 3 described inReference Example E2 was changed from 100° C. to 250° C. and a mixed gasof 12% ammonia/51% nitrogen/37% hydrogen was allowed to pass at a flowrate of 100 SCCM, and the concentration of ammonia and the permeanceratio of ammonia/hydrogen and ammonia/nitrogen of the obtained permeatedgas are shown in Table 28. It was found that when the temperature waschanged from 150° C. to 250° C., the ammonia gas concentration in thegas permeated through the membrane decreased as the temperatureincreased. The ammonia permeance at 250° C. was 7.2×10⁷ [mol/(m²·s·Pa)].This is a higher permeance than RHO and MFI zeolite membrane composites,and this is considered to be because the permeance ratio ofammonia/nitrogen or ammonia/hydrogen is small, and the ammoniapermeation selectivity is low, and the gas permeates through gaps anddefects between zeolite particles.

TABLE 28 100° C. 150° C. 200° C. 250° C. NH₃ concentration in permeatedgas 26% 25% 22% 20% NH₃/N₂ permeance ratio 11 10 8 7 NH₃/H₂ permeanceratio 3 3 2 1

From the above results, it was found that the zeolite membrane compositeof the present invention obtained by Examples E2 and E5 was able tostably and efficiently separate ammonia from a gas mixture composed of aplurality of components including ammonia and hydrogen and/or nitrogento the permeation side with high permeability even under hightemperature conditions exceeding 200° C. On the other hand, in the caseof the zeolite membrane composite obtained by Reference Example E2, itis considered that the ammonia permeation selectivity was deteriorateddue to formation of gaps and defects between zeolite particles due tothermal contraction of zeolite at a temperature higher than 200° C.Specifically, it is considered that, since the change rate of thermalexpansion coefficient at 300° C. with respect to the thermal contractioncoefficient at 30° C. of the CHA zeolite obtained in Reference ExampleE2 was as large as −0.30%, a crack generated at a zeolite grain boundarydue to thermal contraction of zeolite in a high temperature range higherthan 200° C., and the ammonia separation performance deteriorated due togas permeation through the crack. In other words, it was found that, inorder to maintain the high denseness of a zeolite membrane composite ina temperature range higher than 200° C. and to separate ammonia from agas mixture composed of a plurality of components including ammonia andhydrogen and/or nitrogen with high selectivity and high permeability,the film performance deteriorated when the change rate of thermalexpansion coefficient at 300° C. with respect to the thermal expansioncoefficient at 30° C. was changed as small as 0.30%. In contrast, it wasfound that, although, when the change rate of thermal contractioncoefficient at 300° C. with respect to thermal expansion coefficient at30° C. was 0.02% as in the zeolite described in Example E2, the thermalcontraction coefficient at 200° C. was 1.55%, which was a considerablethermal contraction, surprisingly, ammonia permeated with highselectivity in a temperature range higher than 200° C. It was foundthat, as in the zeolites described in Examples E5 and E8, when theabsolute value of the change rate of thermal expansion coefficient at300° C. with respect to thermal expansion coefficient at 30° C. waswithin 0.25%, ammonia permeated with high selectivity in a temperaturerange higher than 200° C.

REFERENCE SIGNS LIST

-   -   1 Zeolite membrane composite    -   2 Pressure vessel    -   3 Sealing portion at tip of support    -   4 Joint between zeolite membrane composite and permeate gas        recovery pipe    -   5 Pressure gauge    -   6 Back pressure valve    -   7 Supply gas (sample gas)    -   8 Permeated gas    -   9 Sweep gas    -   10 Non-permeated gas    -   11 Permeated gas recovery pipe    -   12 Sweep gas supply pipe

1. A method for separating ammonia from a mixed gas comprising ammoniagas, hydrogen gas, and nitrogen gas, the method comprising: contactingthe mixed gas with a zeolite membrane thereby allowing the ammonia gasto selectively permeate the zeolite membrane and separate from the mixedgas, wherein a concentration of the ammonia gas in the mixed gas is 1.0%by volume or more relative to a total volume of the mixed gas, and thezeolite membrane has an SiO₂/Al₂O molar ratio is 6 or more and 500 orless.
 2. The method according to claim 1, wherein a volume ratio ofhydrogen gas/nitrogen gas in the mixed gas is from 0.2 to
 3. 3. Themethod according to claim 1, wherein the temperature at which theammonia gas is separated from the mixed gas is in a range of 50° C. to500° C.
 4. The method according to claim 1, wherein the zeolite membranecomprises RHO zeolite or MFI zeolite.
 5. The method according to claim1, wherein at least a portion of the ammonia gas in the mixed gas isproduced from hydrogen gas and nitrogen gas in the mixed gas.
 6. Themethod according to claim 1, wherein the concentration of the ammoniagas in the mixed gas is 2.0% by volume or more and 60% by volume or lessrelative to the total volume of the mixed gas.
 7. The method accordingto claim 1, wherein the pressure of the mixed gas is 0.1 MPa or more and20 MPa or less
 8. The method according to claim 1, wherein adifferential pressure between the mixed gas and the gas that haspermeated the zeolite membrane is 0.01 MPa or more and 10 MPa.
 9. Themethod according to claim 1, wherein the zeolite membrane is formed bycrystallizing zeolite on a surface of a porous support.
 10. The methodaccording to claim 1, wherein the zeolite membrane is formed on atubular support.
 11. The method according to claim 10, wherein the mixedgas is supplied to the outside of the tubular support on which thezeolite membrane is formed.